put the psymtab filename in the filename bcache

put the psymtab filename in the filename bcache

This puts the psymtab filename in the filename bcache.
This saves a small amount of memory.

2013-12-06  Tom Tromey  <tromey@redhat.com>

	* psymtab.c (allocate_psymtab): Put the filename in the filename
	bcache.