OCL device code - replaced float3* by float*

The host code allocates device buffers of type float3 for (number of
elements * sizeof(float) * 3) bytes, but sizeof(float3) is 4x4 = 16
bytes.
As a consequence, float3* buffers have been replaced by float* buffers
and the access to x, y, z components is done by correctly computing the
index.
x -> new_index = 3 * old_index + 0
y -> new_index = 3 * old_index + 1
z -> new_index = 3 * old_index + 2
Replaced one more sizeof(cl_float3) by sizeof(rvec)
Removed comment
Removed command_queue from ocl_gpu_info_t
Added calls to nbnxn_ocl_free, nbnxn_ocl_wait_gpu

TO DO: add implementation for these functions. They are currently empty.
Merge pull request #1 from StreamComputing/asc

Asc
Moved/added kernel objects to nbnxn_opencl_ptr_t

1. Removed kernel objects from ocl_gpu_info_t
2. Similar for initializations in gpu_utils.cpp
3. Added kernel fields to nbnxn_opencl data structure
4. Added nbnxn_init_kernels
5. Updated select_nbnxn_kernel to work with the kernels from
nbnxn_opencl_ptr_t as a cache
6. Added free_kernels
Merge pull request #2 from StreamComputing/asc

Moved/added kernel objects to nbnxn_opencl_ptr_t
Fixed GPU detection on clients with multiple platforms
Temporary fixes for readbuffer

Made clReadbuffer a synchronous operation as previously GPU wrote while
the host read the same memory segment. In addition removed unnecessary
clFinish calls
Fixed bug in detect_ocl_gpus
Merge pull request #30 from sharpneli/asc

Asc
Correct async wait

Removed blocking read. Implemented waiting on OpenCL
Merge pull request #3 from StreamComputing/asc

Asc
Fixed OpenCL GPU sync to match cuda one

Now correctly performs energy accumulation and shift forces
Merge pull request #33 from sharpneli/asc

Implemented ocl_wait_gpu
Fix compilation in Linux: added missing header