add error checks to all of the OpenCL calls in jni/opencl_aes.c, but
nothing seems to be failing
checking clGetDeviceInfo for CL_DEVICE_AVAILABLE (== CL_TRUE) never
indicates the GPU isn’t available, so crashing still happens in that
case
start sampling AES encryption performance based on size
run experiements on motox.  Change opencl_aes to using 1 work-item for
N/16 work-groups to encrypt an N byte array.  Each work item operates
on a uint4, which is 4 * 32-bit integers (i.e. 16 bytes of the input
array).  Previously implementation used multiple work-items (maximum
available) to operate on the same entry... which was wrong.

Also, don't allocate input/output arrays on the stack (since for around
8MB we will not have enough stackspace and will segfault).  Use malloc.
make the opencl aes kernel split up the array when doing encryption
(specified as second command line parameter).
modify scripts to use global worksize parameter
try varying the local work size, and discovered way better throughput.
allow for new parameters:
- number of work groups
- work group size