[trac] add some anti-spam machinery

[philll]

Background

Apparently, out Trac instance for our ​issue tracker gets spammed more and more, as those examples show:

Ticket	Status	Resolution	Summary
#415	closed	rejected	spam
#456	closed	incomplete	spam
#458	closed	rejected	spam
#470	closed	rejected	Spam
#478	closed	incomplete	spam
#490	closed	incomplete	spam
#502	closed	incomplete	spam
#503	closed	incomplete	spam
#515	closed	rejected	spam
#525	closed	incomplete	spam
#526	closed	incomplete	spam
#528	closed	rejected	spam
#555	closed	incomplete	spam
#557	closed	incomplete	spam
#560	closed	incomplete	spam
#570	closed	incomplete	spam
#574	closed	incomplete	spam
#575	closed	incomplete	spam
#576	closed	incomplete	spam
#578	closed	incomplete	spam
#586	closed	incomplete	spam
#587	closed	incomplete	spam
#588	closed	incomplete	spam
#589	closed	incomplete	spam
#590	closed	incomplete	spam
#593	closed	incomplete	spam
#595	closed	incomplete	spam
#596	closed	incomplete	spam
#597	closed	incomplete	spam
#598	closed	incomplete	spam
#599	closed	incomplete	spam
#602	closed	incomplete	spam
#603	closed	incomplete	spam
#605	closed	incomplete	spam
#606	closed	incomplete	spam
#621	closed	incomplete	spam
#622	closed	incomplete	spam
#623	closed	incomplete	spam
#624	closed	incomplete	spam
#625	closed	incomplete	spam
#626	closed	incomplete	spam
#627	closed	incomplete	spam
#630	closed	incomplete	spam
#631	closed	incomplete	spam
#632	closed	incomplete	spam
#633	closed	incomplete	spam
#634	closed	incomplete	spam
#635	closed	incomplete	spam
#637	closed	incomplete	spam
#638	closed	incomplete	spam
#641	closed	fixed	[trac] false positive spam recognition for new trac registration attempts
#643	closed	incomplete	spam
#668	closed	duplicate	adblock for safari ads spam to the email in outlook
#683	new		Trac: Add whitelist to avoid spam filter.
#699	closed	fixed	[trac] set minimum karma of spambayes to -14
#1157	closed	incomplete	spam
#1329	closed	incomplete	spam
#1493	closed	incomplete	spam
#1690	closed	incomplete	spam
#3407	closed	fixed	Warning "unsafe CPOW usage" spammed to console when list of blockable items is open
#4005	closed	rejected	spam
#4006	closed	rejected	spam
#4007	closed	rejected	Spam
#4323	closed	invalid	spam
#5226	closed	invalid	spam
#5420	closed	invalid	spam
#5684	closed	invalid	spam
#5865	closed	invalid	spam
#6118	closed	invalid	spam
#6181	closed	invalid	spam
#6509	closed	invalid	spam
#6580	closed	invalid	spam
#6642	closed	invalid	spam
#6761	closed	invalid	spam
#6767	closed	invalid	spam
#6817	closed	invalid	spam
#6836	closed	invalid	spam
#6837	closed	invalid	spam
#6934	closed	invalid	spam
#7154	closed	invalid	spam
#7156	closed	invalid	spam
#7184	closed	invalid	spam
#7195	closed	invalid	Spam.
#7280	closed	invalid	spam
#7286	closed	invalid	spam
#7320	closed	invalid	spam
#7323	closed	invalid	spam
#7330	closed	invalid	spam
#7331	closed	invalid	spam
#7332	closed	invalid	spam
#7333	closed	invalid	spam
#7339	closed	invalid	spam
#7349	closed	invalid	spam
#7362	closed	invalid	spam
#7363	closed	invalid	spam
#7364	closed	invalid	spam
#7367	closed	invalid	spam
#7368	closed	invalid	spam
#7369	closed	invalid	spam
#7370	closed	invalid	spam
#7397	closed	rejected	Add "report spam" buttons to this TRAC
#7412	closed	invalid	spam
#7413	closed	invalid	spam
#7414	closed	invalid	spam
#7426	closed	invalid	spam
#7427	closed	invalid	spam
#7464	closed	invalid	spam
#7475	closed	invalid	spam
#7476	closed	invalid	spam
#7477	closed	invalid	spam
#7478	closed	invalid	spam
#7479	closed	invalid	spam
#7481	closed	invalid	spam
#7482	closed	invalid	spam
#7483	closed	invalid	spam
#7484	closed	invalid	spam
#7485	closed	invalid	spam
#7486	closed	invalid	spam
#7487	closed	invalid	spam
#7491	closed	invalid	spam
#7492	closed	invalid	spam
#7493	closed	invalid	spam
#7494	closed	invalid	spam
#7495	closed	invalid	spam
#7496	closed	invalid	spam
#7497	closed	invalid	spam
#7498	closed	invalid	spam
#7499	closed	invalid	spam
#7500	closed	invalid	spam
#7501	closed	invalid	spam
#7502	closed	invalid	spam
#7503	closed	invalid	spam
#7504	closed	invalid	spam
#7505	closed	invalid	spam
#7506	closed	invalid	spam
#7507	closed	invalid	spam
#7508	closed	invalid	spam
#7510	closed	invalid	spam
#7511	closed	invalid	spam
#7513	closed	invalid	spam
#7514	closed	invalid	spam
#7515	closed	invalid	spam
#7516	closed	invalid	spam
#7517	closed	invalid	spam
#7518	closed	invalid	spam
#7519	closed	invalid	spam
#7520	closed	invalid	spam
#7521	closed	invalid	spam
#7522	closed	invalid	spam
#7523	closed	invalid	spam
#7524	closed	invalid	spam
#7525	closed	invalid	spam
#7526	closed	invalid	spam
#7527	closed	invalid	spam
#7528	closed	invalid	spam
#7529	closed	invalid	spam
#7530	closed	invalid	spam
#7531	closed	invalid	spam
#7532	closed	invalid	spam
#7533	closed	invalid	spam
#7534	closed	invalid	spam
#7535	closed	invalid	spam
#7536	closed	invalid	spam
#7537	closed	invalid	spam
#7538	closed	invalid	spam
#7539	closed	invalid	spam
#7540	closed	invalid	spam
#7541	closed	invalid	spam
#7542	closed	invalid	spam
#7543	closed	invalid	spam
#7544	closed	invalid	spam
#7545	closed	invalid	spam
#7546	closed	invalid	spam
#7547	closed	invalid	spam
#7548	closed	invalid	spam
#7549	closed	invalid	spam
#7550	closed	invalid	spam

Until now, our moderators and staff are manually handling those issues, setting them to invalid/rejected. Apparently, this approach is binding valuable workforce.

What to change

Provide some at least semi-automated way of avoiding most of such spam attemps while not badly influencing Trac's functionality.