narrowbundle2: replace map() with equivalent list comprehension

The result of this gets used as a list in core code, so the generator
returned by map() on Python 3 is a problem.

Differential Revision: https://phab.mercurial-scm.org/D2369

hgext/narrow/narrowbundle2.py

@@ -123,7 +123,7 b' def _computeellipsis(repo, common, heads'
     missing = list(cl.findmissingrevs(common=commonrevs, heads=headsrevs))
     visit = reversed(missing)
     relevant_nodes = set()
-    visitnodes = map(cl.node, missing)
+    visitnodes = [cl.node(m) for m in missing]
     required = set(headsrevs) | known
     for rev in visit:
         clrev = cl.changelogrevision(rev)