Fixed RebaseDialog usability improvements

Some RebaseDialog usability improvements were merged to stable-2.11
in [1]. That patch was incompatible with master and got broken
as soon as stable-2.11 was merged with master in [2].

This patch fixes [1] on master.

[1] https://gerrit-review.googlesource.com/#/c/66543/
[2] https://gerrit-review.googlesource.com/#/c/67052/

Change-Id: I9e253bbedc299c198adb06fc32916334511c272d
3 files changed