fix incorrect warning when walking on a particular rev
when a directory was given instead of a file it reported
incorrectly 'No such file or directory in rev <rev>'
we test if the file is a prefix directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolvedremoving babort: update spans branches, use 'hg merge' or 'hg update -C' to lose changes