expandHandleSpace() should check hpoolfreelist before giving up on out of memory

There is a flaw in the garbage collector's code that deals with handles that
I think bears scrutiny. This isn't a showstopper bug, but nevertheless should
get some attention. The problems are described in detail below.

In expandHandleSpace() in gc.c, if it is not possible to expand
handle space at all, the routine gives up on out of memory even if there are
free handles on the hpoolfreelist. It seems to me that the appropriate thing to
do is continue to run under these conditions, because there are still valid
handles in the system. A fix is to check, as a last resort, to see if there
were any handles on the hpoolfreelist before giving up.