Support Mercurial 7.2

In Mercurial 7.2 the iteritems() method of the branchmap has been
removed. Switch to iterating over the branches and then fetching heads
by the branchheads() method. In 7.2, a call to
mercurial.initialization.init() is also needed to process a repo using
the largefiles extension.

Thanks to Michael Cho (@cho-m) for suggesting the initialization fix.

Closes #348

Co-developed-by: Michael Cho <michael@michaelcho.dev>

hg-fast-export.py

@@ -488,7 +488,9 @@ def branchtip(repo, heads):
 
 def verify_heads(ui,repo,cache,force,ignore_unnamed_heads,branchesmap):
   branches={}
-  for bn, heads in repo.branchmap().iteritems():
+
+  for bn in repo.branchmap():
+    heads = repo.branchmap().branchheads(bn)
     branches[bn] = branchtip(repo, heads)
   l=[(-repo.changelog.rev(n), n, t) for t, n in branches.items()]
   l.sort()

hg2git.py

@@ -30,6 +30,14 @@ def set_origin_name(name):
   origin_name = name.encode('utf8')
 
 def setup_repo(url):
+  try:
+    # Mercurial >= 7.2 requires explicit initialization for largefile
+    # support to work.
+    from mercurial import initialization
+    initialization.init()
+  except ImportError:
+    pass
+
   try:
     myui=ui.ui(interactive=False)
   except TypeError: