largefiles: extract test-lfconvert.t from test-largefiles.t
test-largefiles.t is getting pretty big, and there's lots more to test
in lfconvert. And lfconvert is a fairly orthogonal feature to the
rest of largefiles.
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 4 changes to 4 files
updating to branch default
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 4 changes to 4 files
updating to branch default
4 files updated, 0 files merged, 0 files removed, 0 files unresolved