PR# 13760 Garbage collection can be left off if fail to allocate memory or receive a signal

If a run-time routine fails to allocate memory, garbage collection can be
left off in some circumstances.  For example, in pstore.c routine
`parsing_store_append', the call to `traversal' can raise an exception
if it fails to allocate memory.  If this happens and GC was on at
entry to `parsing_store_append', it appears (based on code inspection)
that GC will remain off.  

Another example is in routine `ediso' in equal.c.  If a memory allocation
fails after GC is turned off (or if a signal is delivered and handler
does a longjmp - doesn't look like signals are blocked at this point),
then GC will remain off.  Perhaps you need a generic mechanism to deal
with this kind of problem.

There may be other similar cases, which can be found by searching the
run-time code for "gc_ison" and if GC is turned off, verifying that
it is always turned back on, even if an exception is raised.  You can
also search for "rt_g_data.status" to find other possible areas of code
that need to be checked.