lfs: respect narrowmatcher when testing to add 'lfs' requirement (issue5794)

There's a similar test in lfs.wrapper.convertsink(), but I didn't update that
because I don't think that the sink repo in a convert can be narrow.

It seems reasonable that a narrow clone of an LFS repo may not necessarily be an
LFS repo.  The only potential issue is that LFS has a hard requirement for
changegroup v3, which that extension enables.  The use of treemanifest will
enable changegroup v3 in narrow clones, because allsupportedversions() in
changegroup.py preserves it when it sees a 'treemanifest' requirement.  But I
don't see where changegroup v3 is enabled for a flat manifest.

hgext/lfs/__init__.py

@@ -226,9 +226,11 b' def reposetup(ui, repo):'
                     s = repo.set('%n:%n', _bin(kwargs[r'node']), _bin(last))
                 else:
                     s = repo.set('%n', _bin(kwargs[r'node']))
+            match = repo.narrowmatch()
             for ctx in s:
                 # TODO: is there a way to just walk the files in the commit?
-                if any(ctx[f].islfs() for f in ctx.files() if f in ctx):
+                if any(ctx[f].islfs() for f in ctx.files()
+                       if f in ctx and match(f)):
                     repo.requirements.add('lfs')
                     repo._writerequirements()
                     repo.prepushoutgoinghooks.add('lfs', wrapper.prepush)

tests/test-narrow-commit.t

@@ -28,7 +28,11 b' create full repo'
 
   $ cd ..
 
-  $ hg clone --narrow ssh://user@dummy/master narrow --include inside
+(The lfs extension does nothing here, but this test ensures that its hook that
+determines whether to add the lfs requirement, respects the narrow boundaries.)
+
+  $ hg --config extensions.lfs= clone --narrow ssh://user@dummy/master narrow \
+  >    --include inside
   requesting all changes
   adding changesets
   adding manifests