rearrange struct value to save memory

This patch rearranges struct value a tiny bit, moving the "regnum"
field into a hole.  This saves 8 bytes per value on a 64-bit machine,
and 4 bytes per value on a 32 bit machine.  I think it does not
negatively affect readability or performance.

Built and regtested on x86-64 Fedora 18.

2014-01-16  Tom Tromey  <tromey@redhat.com>

	* value.c (struct value) <regnum>: Move earlier.
daily update
	* dll.c (UNSPECIFIED_CORE_ADDR): New macro.
	(match_dll): Use it.