Currently if we fail to commit memory on linux or solaris we
do a VM exit. This failure has shown up in the nightly testing
in the last few builds. Because of the loss of the reservation
on the memory, this is a reasonable action to take. For background
see

https://jbs.oracle.com/bugs/browse/JDK-6843484

The original problem was

1) GC reserved memory
2) GC tries to commit memory and fails and looses
the reservation on the memory.
3) Other thread gets reserves the memory.
4) GC again tries to commit because it thinks
it still has the memory.

Dan considered reserving the memory again after 2)
but there would be a race with 3) so instead calls
a VM exit.

Should we consider after 2) reducing the size of
the VirtualSpace so that GC does not try to do
4)?