Catch BadName exceptions from newer GitPython

Catch the BadName exception raised by newer GitPython and gitdb versions
while ensuring that we still retain compatibility with older versions
that did not either contain this exception nor raise it.

To handle a new exception where it doesn't exist in the older codebase
simply set the value to None as except has no problem in matching
against non-existing exceptions.

Change-Id: Idf1f3e776317ad7a346364b9fadb4bc613bf2673

git_upstream/commands/drop.py

@@ -25,6 +25,11 @@ from git import BadObject
 import inspect
 import re
 
+try:
+    from git import BadName
+except ImportError:
+    BadName = None
+
 
 class DropError(GitUpstreamError):
     """Exception thrown by L{Drop}"""
@@ -60,7 +65,7 @@ class Drop(LogDedentMixin, GitMixin):
         try:
             # test commit "id" presence
             self._commit = self.repo.commit(git_object)
-        except BadObject:
+        except (BadName, BadObject):
             raise DropError(
                 "Commit '%s' not found (or ambiguous)" % git_object)
 

git_upstream/commands/supersede.py

@@ -27,6 +27,11 @@ from git import BadObject, Head
 import inspect
 import re
 
+try:
+    from git import BadName
+except ImportError:
+    BadName = None
+
 
 class SupersedeError(GitUpstreamError):
     """Exception thrown by L{Supersede}"""
@@ -78,7 +83,7 @@ class Supersede(LogDedentMixin, GitMixin):
         try:
             # test commit "id" presence
             self._commit = self.repo.commit(git_object)
-        except BadObject:
+        except (BadName, BadObject):
             raise SupersedeError("Commit '%s' not found (or ambiguous)" %
                                  git_object)