mergetool-lib: make the three-way diff the default for vim/gvim

The original vimdiff/gvimdiff configuration is now available by using
'vimdiff2' or 'gvimdiff2' as the preferred merge tool.

Signed-off-by: Dan McGee <dpmcgee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-mergetool--lib.sh

@@ -10,10 +10,10 @@ merge_mode() {
 
 translate_merge_tool_path () {
 	case "$1" in
-	vimdiff)
+	vimdiff|vimdiff2)
 		echo vim
 		;;
-	gvimdiff)
+	gvimdiff|gvimdiff2)
 		echo gvim
 		;;
 	emerge)
@@ -47,7 +47,8 @@ check_unchanged () {
 valid_tool () {
 	case "$1" in
 	kdiff3 | tkdiff | xxdiff | meld | opendiff | \
-	emerge | vimdiff | gvimdiff | ecmerge | diffuse | araxis | p4merge)
+	vimdiff | gvimdiff | vimdiff2 | gvimdiff2 | \
+	emerge | ecmerge | diffuse | araxis | p4merge)
 		;; # happy
 	tortoisemerge)
 		if ! merge_mode; then
@@ -185,6 +186,17 @@ run_merge_tool () {
 				"$LOCAL" "$REMOTE"
 		fi
 		;;
+	vimdiff2|gvimdiff2)
+		if merge_mode; then
+			touch "$BACKUP"
+			"$merge_tool_path" -f -d -c "wincmd l" \
+				"$LOCAL" "$MERGED" "$REMOTE"
+			check_unchanged
+		else
+			"$merge_tool_path" -f -d -c "wincmd l" \
+				"$LOCAL" "$REMOTE"
+		fi
+		;;
 	xxdiff)
 		if merge_mode; then
 			touch "$BACKUP"