Update arc-hg to support mercurial 6.1

Summary:
Updated the mercurial script to pull the `parseurl` function from the new module if pulling from the old module fails.

Also updated pulling of `remoteopts` to follow the same pattern of fallback.

Fixes T13672

Test Plan:
Using mercurial 6.1 I ran `arc patch Dnnnnn --trace` and verified that it succeeded and in the trace output it used the `arc-ls-markers` extension.

Using mercurial 4.7 I ran `arc patch Dnnnnn --trace` and verified that it succeeded and in the trace output it used the `arc-ls-markers` extension.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Maniphest Tasks: T13672

Differential Revision: https://secure.phabricator.com/D21747

support/hg/arc-hg.py

@@ -39,12 +39,17 @@ except:
   command = cmdutil.command(cmdtable)
 
 try:
-  if "remoteopts" in cmdutil:
+  remoteopts = cmdutil.remoteopts
-    remoteopts = cmdutil.remoteopts
 except:
   from mercurial import commands
   remoteopts = commands.remoteopts
 
+try:
+  parseurl = hg.parseurl
+except:
+  from mercurial import utils
+  parseurl = utils.urlutil.parseurl
+
 @command(
   b'arc-amend',
   [
@@ -268,7 +273,7 @@ def remotemarkers(ui, repo, source, opts):
 
   markers = []
 
-  source, branches = hg.parseurl(ui.expandpath(source))
+  source, branches = parseurl(ui.expandpath(source))
   remote = hg.peer(repo, opts, source)
 
   with remote.commandexecutor() as e: