mergetools: fix xxdiff hotkeys

xxdiff was using a mix of "Ctrl-<key>" and "Ctrl+<key>" hotkeys.
The dashed "-" form is not accepted by newer xxdiff versions.
Use the plus "+" form only.

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

mergetools/xxdiff

@@ -1,7 +1,7 @@
 diff_cmd () {
 	"$merge_tool_path" \
 		-R 'Accel.Search: "Ctrl+F"' \
-		-R 'Accel.SearchForward: "Ctrl-G"' \
+		-R 'Accel.SearchForward: "Ctrl+G"' \
 		"$LOCAL" "$REMOTE"
 }
 
@@ -10,15 +10,15 @@ merge_cmd () {
 	if $base_present
 	then
 		"$merge_tool_path" -X --show-merged-pane \
-			-R 'Accel.SaveAsMerged: "Ctrl-S"' \
+			-R 'Accel.SaveAsMerged: "Ctrl+S"' \
 			-R 'Accel.Search: "Ctrl+F"' \
-			-R 'Accel.SearchForward: "Ctrl-G"' \
+			-R 'Accel.SearchForward: "Ctrl+G"' \
 			--merged-file "$MERGED" "$LOCAL" "$BASE" "$REMOTE"
 	else
 		"$merge_tool_path" -X $extra \
-			-R 'Accel.SaveAsMerged: "Ctrl-S"' \
+			-R 'Accel.SaveAsMerged: "Ctrl+S"' \
 			-R 'Accel.Search: "Ctrl+F"' \
-			-R 'Accel.SearchForward: "Ctrl-G"' \
+			-R 'Accel.SearchForward: "Ctrl+G"' \
 			--merged-file "$MERGED" "$LOCAL" "$REMOTE"
 	fi
 	check_unchanged