git-svn: Don't create a "master" branch every time rebase is run

If you run "git-svn rebase" while sitting on a topic branch, there is
no need to create a "master" branch if one didn't exist already. The
branch was created implicitly by the automatic checkout after fetching,
which in the case of rebase isn't actually necessary anyway.

Signed-off-by: Steven Grimm <koreth@midwinter.com>
Acked-by: Eric Wong <normalperson@yhbt.net>

git-svn.perl

@@ -550,6 +550,8 @@ sub cmd_rebase {
 		exit 1;
 	}
 	unless ($_local) {
+		# rebase will checkout for us, so no need to do it explicitly
+		$_no_checkout = 'true';
 		$_fetch_all ? $gs->fetch_all : $gs->fetch;
 	}
 	command_noisy(rebase_cmd(), $gs->refname);