merge with stable

fileset: replace predicate by filesetpredicate of registrar (API) To make all built-in predicates be known to hggettext, loading built-in predicates by loadpredicate() should be placed before fixing i18nfunctions but after all of predicate decorating.

registrar: add filesetpredicate to mark a function as fileset predicate filesetpredicate is used to replace fileset.predicate in subsequent patch. This patch also adds loadpredicate() to fileset, because this combination helps to figure out how the name of "status caller" (or "existing caller") predicate is put into _statuscallers (or _existingcallers). Listing up loadpredicate() in dispatch.extraloaders causes implicit loading fileset predicate functions at loading (3rd party) extension.

registrar: remove useless base classes (API) Previous patches make these classes useless by removing classes derived from them.

revset: remove useless extpredicate class (API) Previous patch makes this classes useless by replacing it with revsetpredicate of registrar. BTW, extpredicate itself has already been broken by that patch, because revsetpredicate of registrar doesn't have compatibility with original predicate (derived from funcregistrar of registrar), in fact.

hook: filter out unstable output in tests This output is different between Python 2.6 and Python 2.7. It's also pretty irrelevant, so just filter it out.