mergetool: rename bc3 to bc

Beyond Compare version 4 works the same way as version 3, so rename
the existing "bc3" adaptor to just "bc", while keeping "bc3" as a
backward compatible wrapper.

Noticed-by: Olivier Croquette <ocroquette@free.fr>
Helped-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

mergetools/bc

@@ -0,0 +1,25 @@
+diff_cmd () {
+	"$merge_tool_path" "$LOCAL" "$REMOTE"
+}
+
+merge_cmd () {
+	touch "$BACKUP"
+	if $base_present
+	then
+		"$merge_tool_path" "$LOCAL" "$REMOTE" "$BASE" \
+			-mergeoutput="$MERGED"
+	else
+		"$merge_tool_path" "$LOCAL" "$REMOTE" \
+			-mergeoutput="$MERGED"
+	fi
+	check_unchanged
+}
+
+translate_merge_tool_path() {
+	if type bcomp >/dev/null 2>/dev/null
+	then
+		echo bcomp
+	else
+		echo bcompare
+	fi
+}

mergetools/bc3

@@ -1,25 +1 @@
-diff_cmd () {
-	"$merge_tool_path" "$LOCAL" "$REMOTE"
-}
-
-merge_cmd () {
-	touch "$BACKUP"
-	if $base_present
-	then
-		"$merge_tool_path" "$LOCAL" "$REMOTE" "$BASE" \
-			-mergeoutput="$MERGED"
-	else
-		"$merge_tool_path" "$LOCAL" "$REMOTE" \
-			-mergeoutput="$MERGED"
-	fi
-	check_unchanged
-}
-
-translate_merge_tool_path() {
-	if type bcomp >/dev/null 2>/dev/null
-	then
-		echo bcomp
-	else
-		echo bcompare
-	fi
-}
+. "$MERGE_TOOLS_DIR/bc"