mergetools: add support for smerge (Sublime Merge)

Teach difftool and mergetool about the Sublime Merge "smerge" command.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-mergetool--lib.sh

@@ -279,6 +279,7 @@ list_merge_tool_candidates () {
 		fi
 		tools="$tools gvimdiff diffuse diffmerge ecmerge"
 		tools="$tools p4merge araxis bc codecompare"
+		tools="$tools smerge"
 	fi
 	case "${VISUAL:-$EDITOR}" in
 	*vim*)

mergetools/smerge

@@ -0,0 +1,12 @@
+diff_cmd () {
+	"$merge_tool_path" mergetool "$LOCAL" "$REMOTE" -o "$MERGED"
+}
+
+merge_cmd () {
+	if $base_present
+	then
+		"$merge_tool_path" mergetool "$BASE" "$LOCAL" "$REMOTE" -o "$MERGED"
+	else
+		"$merge_tool_path" mergetool "$LOCAL" "$REMOTE" -o "$MERGED"
+	fi
+}