bash: Support git-rebase -m continuation completion.

Apparently git-rebase -m uses a metadata directory within .git (.git/.dotest-merge) rather than .dotest used by git-am (and git-rebase without the -m option). This caused the completion code to not offer --continue, --skip or --abort when working within a git-rebase -m session.

---
 contrib/completion/git-completion.bash |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 466cc32..5f9a34b 100755
@@ -627,7 +627,7 @@ _git_push ()
 _git_rebase ()
 {
 	local cur="${COMP_WORDS[COMP_CWORD]}"
-	if [ -d .dotest ]; then
+	if [ -d .dotest ] || [ -d .git/.dotest-merge ]; then
 		__gitcomp "--continue --skip --abort"
 		return
 	fi

1.5.0.rc3.39.gec804