Merge branch 'nd/rebase-show-current-patch'

The new "--show-current-patch" option gives an end-user facing way
to get the diff being applied when "git rebase" (and "git am")
stops with a conflict.

* nd/rebase-show-current-patch:
  rebase: introduce and use pseudo-ref REBASE_HEAD
  rebase: add --show-current-patch
  am: add --show-current-patch

t/t3404-rebase-interactive.sh

@@ -225,6 +225,14 @@ test_expect_success 'stop on conflicting pick' '
 	test 0 = $(grep -c "^[^#]" < .git/rebase-merge/git-rebase-todo)
 '
 
+test_expect_success 'show conflicted patch' '
+	GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
+	grep "show.*REBASE_HEAD" stderr &&
+	# the original stopped-sha1 is abbreviated
+	stopped_sha1="$(git rev-parse $(cat ".git/rebase-merge/stopped-sha"))" &&
+	test "$(git rev-parse REBASE_HEAD)" = "$stopped_sha1"
+'
+
 test_expect_success 'abort' '
 	git rebase --abort &&
 	test $(git rev-parse new-branch1) = $(git rev-parse HEAD) &&