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.

adding foo
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
pushing to ../2
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files