conditional testing of SharedArray

In certain cases, the shared memory segments created were not being unlinked cleanly. I have made the sharedarray test conditional for now.

On linux, you can manually do a `rm /dev/shm/jl*` . On OSX you will need a reboot. Sorry about this, calling shm_unlink from a remotecall seems to be ineffective. I have disabled the tests till it is fixed.