convert: correctly detect missing revlog for root revisions

convert: ignore hg source errors with hg.ignoreerrors (issue 1357) This flag makes missing revlog errors to be ignored which allow broken repositories to be fixed by converting them from and to Mercurial.

grep: avoid infinite loop when trailing newline is missing

introduce fncache repository layout * adds a new entry 'fncache' to '.hg/requires' for new repos * writes new file '.hg/store/fncache' * hash-encodes filenames with long paths (issue839) * encodes Windows reserved filenames (issue793)

bisect with command: ability to skip revision or abort bisection

bisect: ability to check revision with command

Make it possible to disable filtering for a pattern. Rationale: Apparently there were no way to disable for example win32text extension locally. RFC: Can it already be done another way?

i18n: import _ instead of gettext

Minor cleanup: Add missing space forgotten in recent change.

Merge with crew-stable