Revert r46447 in Collection -- fixed bug in Categoryfinder class it was trying to...

Revert r46447 in Collection -- fixed bug in Categoryfinder class it was trying to work around.
Categoryfinder::seed() was passing category names through Title::newFromText($ct,NS_CATEGORY), which meant that if the name started with what looks like a namespace, that would override the NS_CATEGORY default.
Thus you got 'Wikipedia:Books' -> text portion 'Books' when you wanted 'Category:Wikipedia:Books' -> text portion 'Wikipedia:Books'.
Using Title::makeTitleSafe(NS_CATEGORY,$ct) instead forces it to always use the category namespace.
Additionally, I've added a check for invalid input -- previously a bad input leading to an invalid title would just kill it dead with a fatal error. Invalid input in the category list is now skipped.