performance: do not stat() things when not required
Ignore unknown files if we don't need them (eg in hg diff).
It slows things down a little bit for big trees (kernel repo), since _join()
is called for each file instead of for each directory.
fix issue567
adding a
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
committer test 0 0
revision 0
branch default
adda