Add `git cl checkout` to checkout by Rietveld issue

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index aef7c4ff93c0738a74e4a2d81fd1d16934208249..8b33d6e529ca4e64fa2bd7302c8328373e7992b7 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -3541,6 +3541,49 @@ def CMDformat(parser, args):
   return return_value
 
 
+@subcommand.usage('<codereview url or issue id>')
+def CMDco(parser, args):

[Dirk Pranke, 2015/09/22 17:52:34]

it seems like this should probably be CMDcheckout, even though I hate typing
longer things :(.

[scottmg, 2015/09/22 17:57:23]

Done.

+  """Checks out a branch associated with a given Rietveld issue."""
+  _, args = parser.parse_args(args)
+
+  if len(args) != 1:
+    parser.print_help()
+    return 1
+
+  if re.match(r'\d+', args[0]):
+    target_issue = args[0]
+  elif args[0].startswith('http'):
+    target_issue = re.sub(r'.*/(\d+)/?', r'\1', args[0])
+  else:
+    parser.print_help()
+    return 1
+
+  key_and_issues = [x.split() for x in RunGit(
+      ['config', '--local', '--get-regexp', r'branch\..*\.rietveldissue'])
+      .splitlines()]
+  branches = []
+  for key, issue in key_and_issues:
+    if issue == target_issue:
+      branches.append(re.sub(r'branch\.(.*)\.rietveldissue', r'\1', key))
+
+  if len(branches) == 1:
+    RunGit(['checkout', branches[0]])
+  else:

[Dirk Pranke, 2015/09/22 17:52:34]

what if there's no match?

[scottmg, 2015/09/22 17:57:23]

Done.

+    print 'Multiple branches match issue %s:' % target_issue
+    for i in range(len(branches)):
+      print '%d: %s' % (i, branches[i])
+    which = raw_input('Choose by index: ')
+    try:
+      RunGit(['checkout', branches[int(which)]])
+    except (IndexError, ValueError):
+      print 'Invalid selection, not checking out any branch.'
+      return 1
+
+  cl = Changelist()
+  print 'Issue number: %s (%s)' % (cl.GetIssue(), cl.GetIssueURL())

[Dirk Pranke, 2015/09/22 17:52:34]

Why print anything? You told it the issue number on the command line.

[scottmg, 2015/09/22 17:57:23]

Done.

+  return 0
+
+
 def CMDlol(parser, args):
   # This command is intentionally undocumented.
   print zlib.decompress(base64.b64decode(