Fix clGetDeviceInfo's CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE case

device->max_constant_buffer_size is cl_ulong not cl_uint
Remove some stale references to USE_LLVM_API
Merge pull request #88 from franz/minor_bugfixes

Fix CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE
Correct kernel routines maxmag, minmag, nan, and rootn
Correct argument types in kernel template for pown and rootn
Use float builtins (instead of double builtins) for half kernel functions

Clang does not support half builtins yet.
Define half constants more elegantly
Merge branch 'master' into fp16-api