rebase: remove bailifchanged check from pullrebase (BC)

This saves us a relatively superfluous status check for pull --rebase (if
rebase runs, it'll check for a clean working directory anyway), and brings hg
pull --rebase closer to hg pull && hg rebase.

This is a behavior change because pull --rebase with a dirty working directory
will now abort after performing the pull rather than before.

hgext/rebase.py

@@ -769,7 +769,6 b' def pullrebase(orig, ui, repo, *args, **'
                      'the update flag\n')
 
         movemarkfrom = repo['.'].node()
-        cmdutil.bailifchanged(repo)
         revsprepull = len(repo)
         origpostincoming = commands.postincoming
         def _dummy(*args, **kwargs):