Rebase on pull should check if branch configuration has rebase set to
true. This is important to correctly abort operation when conflicts
appear, and user chooses not to run mergetool

Change-Id: I365aa534bdbece466514f542ea2e3c371c89a4a8
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>