Add support to git-branch to show local and remote branches

Add support to git-branch to show local and remote branches

Instead of storing a list of refnames in append_ref, a list of
structures is created.  Each of these stores the refname and a
symbolic constant representing its type.

The creation of the list is filtered based on a command line
switch; no switch means "local branches only", "-r" means "remote
branches only" (as they always did); but now "-a" means "local
branches or remote branches".

As a side effect, the list is now not global, but allocated in
print_ref_list() where it used.

Also a memory leak is plugged, the memory allocated during the
list creation was never freed.

It lays a groundwork to also display tags, but the command being
'git branch' it is not currently used.

Signed-off-by: Andy Parkins <andyparkins@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>