[PATCH] Enable and fix support for base less merges.

Let the merge strategies handle the base less case if they are able to
do it. It also fixes git-resolve.sh to die if no common ancestors
exists, instead of doing the wrong thing. Furthermore, it contains a
small independent fix for git-merge.sh and a fix for a base less code
path in gitMergeCommon.py.

With this it's possible to use
    git merge -s recursive 'merge message' A B
to do a base less merge of A and B.

[jc: Thanks Fredrik for fixing the brown-paper-bag in git-merge.
 I fixed a small typo in git-merge-resolve fix; 'test' equality
 check is spelled with single equal sign -- C-style double equal
 sign is bashism.]
Signed-off-by: NFredrik Kuivinen <freku045@student.liu.se>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-merge-resolve.sh

@@ -31,6 +31,12 @@ case "$remotes" in
 	exit 2 ;;
 esac
 
+# Give up if this is a baseless merge.
+if test '' = "$bases"
+then
+	exit 2
+fi
+
 git-update-index --refresh 2>/dev/null
 git-read-tree -u -m $bases $head $remotes || exit 2
 echo "Trying simple merge."

git-merge.sh

@@ -26,7 +26,7 @@ dropsave() {
 savestate() {
 	# Stash away any local modifications.
 	git-diff-index -r -z --name-only $head |
-	cpio -0 -o >"$GIR_DIR/MERGE_SAVE"
+	cpio -0 -o >"$GIT_DIR/MERGE_SAVE"
 }
 
 restorestate() {
@@ -103,7 +103,7 @@ echo "$head" >"$GIT_DIR/ORIG_HEAD"
 
 case "$#,$common" in
 *,'')
-	die "Unable to find common commit between $head_arg and $*"
+	# No common ancestors found. We need a real merge.
 	;;
 1,"$1")
 	# If head can reach all the merge then we are up to date.

gitMergeCommon.py

@@ -213,7 +213,7 @@ def buildGraph(heads):
 
 # Write the empty tree to the object database and return its SHA1
 def writeEmptyTree():
-    tmpIndex = os.environ['GIT_DIR'] + '/merge-tmp-index'
+    tmpIndex = os.environ.get('GIT_DIR', '.git') + '/merge-tmp-index'
     def delTmpIndex():
         try:
             os.unlink(tmpIndex)