filterfiles: Search as long as the target is a prefix of current. filterfiles was failing to find files for directory arguments if another file existed that started with the directory name and sorted earlier. For example, a manifest of ('foo.h', 'foo/foo') would cause filterfiles('foo') to return nothing. This resolves issue #294.

1 files updated, 0 files merged, 0 files removed, 0 files unresolved
removing b
this update spans a branch affecting the following files:
 b
aborting update spanning branches!
(use 'hg merge' to merge across branches or 'hg update -C' to lose changes)