bash: use __gitdir when completing 'git rebase' options
bash: use __gitdir when completing 'git rebase' options

When doing completion of rebase options in a subdirectory of the work
tree during an ongoing rebase, wrong options were offered because of the
hardcoded .git/.dotest-merge path.

Signed-off-by: SZEDER Gábor <46692b1f0516358b02a6405518c0a52aa8fb3e94@ira.uka.de>
Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git