[HAVE_SYS_PSTAT_H]: Include <sys/pstat.h>.

[HAVE_SYS_PSTAT_H]: Include <sys/pstat.h>.
(physmem_total) [HAVE_PSTAT_GETSTATIC]: If sysconf couldn't be used to
determine the amount of total physical memory, use pstat_getstatic.
HPUX-11 doesn't define _SC_PHYS_PAGES.
(physmem_available) [HAVE_PSTAT_GETSTATIC && HAVE_PSTAT_GETDYNAMIC]:
If sysconf couldn't be used to determine the amount of available
physical memory, use both pstat_getstatic and pstat_getdynamic.
Based on a patch from Bob Proulx.