more date-parsing fixing, new sensing method.

Went looking for why alerts weren't happening. didn't find it.
Noticed the mtime could be off by an hour or a day -- fixed it to parse text timezones and do daylight savings properly.  did you know some python timezone routines use 'east of GMT' and some use 'west of GMT' as positive integers?  goddamn.

Also, because I work too hard, I added something to sense a change in url when doing a chain.  Used for SBaHJ and for a new "there's a new sticky on HSG" thing.