git-gui: Allow git-merge to use branch names in conflict markers

Earlier when I rewrote the merge implementation for git-gui I broke
it such that the conflict markers for the "theirs" side of the hunk
was using a full SHA-1 ID in hex, rather than the name of the branch
the user had merged.  This was because I got paranoid and passed off
the full SHA-1 to git-merge, instead of giving it the reference name
the user saw in the merge dialog.

I'd still like to resolve the SHA-1 upfront in git-gui and always use
that value throughout the merge, but I can't do that until we have a
full implementation of git-merge written in Tcl.  Until then its more
important that the conflict markers be useful to the end-user, so we
need to pass off the ref name and not the SHA-1 ID.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

lib/merge.tcl

@@ -114,7 +114,7 @@ method _start {} {
 	lappend cmd --strategy=recursive
 	lappend cmd [git fmt-merge-msg <[gitdir FETCH_HEAD]]
 	lappend cmd HEAD
-	lappend cmd $cmit
+	lappend cmd $name
 
 	set msg "Merging $current_branch and $stitle"
 	ui_status "$msg..."