Due to the complexities of handling .gitignores, rely directly on
git-ls-files rather than a custom gitignore-aware directory walking
routine.
As a side-effect, there has been a minor behaviorial change related to
locking. Previously, if a file was locked, then a matching pattern was
added to a .gitignore, that file was no longer considered locked and the
writeable attribute was set on that file. With this change, files which
match a .gitignore, but have been addded to the repository,
will still have their write bit cleared.
Fixes#3797
83d7f76e76