Use default rebase during sync instead of rebase -i

rebase interactive (aka rebase -i) has changed in newer versions
of git, and doesn't always generate the sequence of commits the
same way it used to.  It also doesn't handle having a previously
applied commit try to be applied again.

The default rebase algorithm is better suited to our needs.
It uses --ignore-if-in-upstream when generating the patch series
for git-am, and git-am with its 3-way fallback is able to handle
a rename case just as well as the cherry-pick variant used by -m.
Its also a generally faster implementation.

Signed-off-by: Shawn O. Pearce <sop@google.com>

project.py

@@ -893,11 +893,11 @@ class Project(object):
       raise GitError('%s reset --hard %s ' % (self.name, rev))
 
   def _Rebase(self, upstream, onto = None):
-    cmd = ['rebase', '-i']
+    cmd = ['rebase']
     if onto is not None:
       cmd.extend(['--onto', onto])
     cmd.append(upstream)
-    if GitCommand(self, cmd, disable_editor=True).Wait() != 0:
+    if GitCommand(self, cmd).Wait() != 0:
       raise GitError('%s rebase %s ' % (self.name, upstream))
 
   def _FastForward(self, head):