BibMatch: validation fixes

• Fixes a bug with match validation that may cause records to be treated as matched, when it should not match. More specifically when matching in the so-called "joker" mode.

• Exposes a new config variable from the matching validation, CFG_BIBMATCH_MIN_VALIDATION_COMPARISONS which dictates the minimum about of matched fields to actually brand it as an equal match.

BibMatch: checks for mechanize in regression tests

BibMatch: improve validator record download

• Previously possible matches were downloaded one-by-one, this patch changes this to only make one query to the server.

BibMatch: adds more logging points