RepoPick : Add support for git pull

Allow user to git pull patchsets and dependencies.

Change-Id: If5520b45fe79836eac628b3caf0526f11f8953d9
(cherry picked from commit df646304bdcef329e3fe7c12b68107de1f4cd42a)
Merge "RepoPick : Add support for git pull" into cm-11.0
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_build into cm-11.0