The hglib Mercurial finder was nice. But it is somewhat slow, as it
involves a separate Mercurial process.
This commit introduces a native Mercurial finder that speaks directly
to a Mercurial repository instance. It is significantly faster.
The new code is isolated to its own file because it imports Mercurial
code, which is GPL.
--HG--
extra : commitid : 8CzDFt3lQmx
extra : rebase_source : 1540ad20d795086926b316612062e2a1f10c4958