Provide a friendlier error message after Rietveld issue deletion.

git_cl.py

Index: git_cl.py
===================================================================
--- git_cl.py	(revision 116333)
+++ git_cl.py	(working copy)
@@ -513,7 +513,19 @@
     issue = ConvertToInteger(self.GetIssue())
     patchset = ConvertToInteger(self.GetPatchset())
     if issue:
-      description = self.GetDescription()
+      try:
+        description = self.GetDescription()
+      except urllib2.HTTPError, e:

[M-A Ruel, 2012/01/04 17:56:51]

I'd prefer to have this at line 448 so all calls would be properly handled.

+        if e.code == 404:
+          DieWithError(
+              ('\nWhile fetching the description for issue %d, received a 404\n'
+               '(not found) error. It is likely that you deleted this issue\n'
+               'on the server. If this is the case, please run\n'
+               '    git cl issue 0\n'
+               'to clear the association with the deleted issue, and then run\n'
+               'this command again.') % issue)
+        else:
+          DieWithError('\nFailed to fetch description. HTTP error ' + e.code)
     else:
       # If the change was never uploaded, use the log messages of all commits
       # up to the branch point, as git cl upload will prefill the description