merge-one-file: use common as base, instead of emptiness.

Unlike the previous round that merged the path added differently
in each branches using emptiness as the base, compute a common
version and use it as input to 'merge' program.

This would show the resulting (still conflicting) file left in
the working tree as:

	common file contents...
	<<<<<< FILENAME
	version from our branch...
	======
	version from their branch...
	>>>>>> .merge_file_XXXXXX
	more common file contents...

when both sides added similar contents.

Signed-off-by: Junio C Hamano <junkio@cox.net>

apply.c

@@ -23,6 +23,7 @@ static int numstat = 0;
 static int summary = 0;
 static int check = 0;
 static int apply = 1;
+static int no_add = 0;
 static int show_index_info = 0;
 static int line_termination = '\n';
 static const char apply_usage[] =
@@ -1112,8 +1113,10 @@ static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag)
 				break;
 		/* Fall-through for ' ' */
 		case '+':
-			memcpy(new + newsize, patch + 1, plen);
-			newsize += plen;
+			if (*patch != '+' || !no_add) {
+				memcpy(new + newsize, patch + 1, plen);
+				newsize += plen;
+			}
 			break;
 		case '@': case '\\':
 			/* Ignore it, we already handled it */
@@ -1710,6 +1713,10 @@ int main(int argc, char **argv)
 			excludes = x;
 			continue;
 		}
+		if (!strcmp(arg, "--no-add")) {
+			no_add = 1;
+			continue;
+		}
 		if (!strcmp(arg, "--stat")) {
 			apply = 0;
 			diffstat = 1;

git-merge-one-file.sh

@@ -57,18 +57,20 @@ case "${1:-.}${2:-.}${3:-.}" in
 # Modified in both, but differently.
 #
 "$1$2$3" | ".$2$3")
+	src2=`git-unpack-file $3`
 	case "$1" in
 	'')
 		echo "Added $4 in both, but differently."
+		# This extracts OUR file in $orig, and uses git-apply to
+		# remove lines that are unique to ours.
 		orig=`git-unpack-file $2`
-		: >$orig
+		diff -u -La/$orig -Lb/$orig $orig $src2 | git-apply --no-add 
 		;;
 	*)
 		echo "Auto-merging $4."
 		orig=`git-unpack-file $1`
 		;;
 	esac
-	src2=`git-unpack-file $3`
 
 	# We reset the index to the first branch, making
 	# git-diff-file useful