clean up the hash entry code a bit. Got rid of lp_shmem_hash_size()

clean up the hash entry code a bit. Got rid of lp_shmem_hash_size()
and made it private to the 2 shmem implementations. Added new
shmops->hash_size() function.

Added code to handle the IPC system limits by looping decreasing the
size of the resources (semaphores and shared memory) that we request
until we get under the system limits, which can be quite low on some
systems!

Added checks that the creator of the IPC objects is root. Otherwise we
would be open to a security hole where someone pre-creates the shared
memory segment and attaches.