git: separate author and committer

Git has the ability to track the person who
creates a commit separately from the person
who wrote the commit. For git9, we ignored
this feature.

However, as we start using git/import more,
it will be useful to figure out who imported
a commit, as well as who wrote it.

This change adds support for seeing this
information in git, as well as setting the
author and committer separately in git/import.

sys/src/cmd/git/merge

@@ -12,7 +12,7 @@ fn merge{
 		ours=$ourbr/$f
 		base=$basebr/$f
 		theirs=$theirbr/$f
-		merge1 ./$f $theirs $base $ours
+		merge1 ./$f $ours $base $theirs
 	}
 }