simplify target_is_pushed

simplify target_is_pushed

While working on target_is_pushed, I noticed that it is written in a
strange way.  The code currently keeps an extra indirection, where a
simple linked list traversal is all that is needed.  It seems likely
this was done by copying and pasting other code.  However, there is no
reason to do this and the more obvious code is simpler to reason
about.  So, this patch change the implementation.

2014-07-29  Tom Tromey  <tromey@redhat.com>

	* target.c (target_is_pushed): Simplify.