vfs: use 'vfs' module directly in 'mercurial.patch'

Now that the 'vfs' classes moved in their own module, lets use the new module
directly. We update code iteratively to help with possible bisect needs in the
future.

mercurial/patch.py

@@ -38,6 +38,7 b' from . import ('
     scmutil,
     similar,
     util,
+    vfs as vfsmod,
 )
 stringio = util.stringio
 
@@ -449,7 +450,7 b' class abstractbackend(object):'
 class fsbackend(abstractbackend):
     def __init__(self, ui, basedir):
         super(fsbackend, self).__init__(ui)
-        self.opener = scmutil.vfs(basedir)
+        self.opener = vfsmod.vfs(basedir)
 
     def _join(self, f):
         return os.path.join(self.opener.base, f)
@@ -560,7 +561,7 b' class filestore(object):'
         else:
             if self.opener is None:
                 root = tempfile.mkdtemp(prefix='hg-patch-')
-                self.opener = scmutil.vfs(root)
+                self.opener = vfsmod.vfs(root)
             # Avoid filename issues with these simple names
             fn = str(self.created)
             self.opener.write(fn, data)