changegroup: avoid shadowing a set with an int

This confuses the heck out of pytype, and I basically agree with it
that this shadowing is confusing. There's a chance this causes some
memory to be freed later, but I think it's probably not worth worrying
about for now.

Differential Revision: https://phab.mercurial-scm.org/D7292

mercurial/changegroup.py

@@ -315,15 +315,15 b' class cg1unpacker(object):'
             )
             self.callback = progress.increment
 
-            efiles = set()
+            efilesset = set()
 
             def onchangelog(cl, node):
-                efiles.update(cl.readfiles(node))
+                efilesset.update(cl.readfiles(node))
 
             self.changelogheader()
             deltas = self.deltaiter()
             cgnodes = cl.addgroup(deltas, csmap, trp, addrevisioncb=onchangelog)
-            efiles = len(efiles)
+            efiles = len(efilesset)
 
             if not cgnodes:
                 repo.ui.develwarn(