No longer block on possible bad branch names.

This is because we cannot confidently check if we are pushing
to a fork or not.
Instead give a warning, and proceed.

Signed-off-by: Troy Dawson <tdawson@redhat.com>

src/centpkg/__init__.py

@@ -92,7 +92,7 @@ class DistGitDirectory(object):
                           DeprecationWarning)
         else:
             if not self.is_fork():
-                raise ValueError("Branchname: {0} is not valid".format(branchtext))
+                warnings.warn('Unable to determine if this is a fork or not. Proceeding, but you should double check.')
             else:
                 self.distrobranch = True
                 self.signame = 'centos'