Fix CUDA on Mac OS X. Fix CUDA in conjunction with mpifake.

nvcc on OS X compiles 32-bit binaries even on 64-bit systems. So check whether we're compiling for 64-bit Macs and set -m64 accordingly.

Use -I./mpifake instead of -I/usr/include/mpi in nvcc flags if compiling with mpifake.
Merge pull request #108 from mkuron/configure-osx

Fix CUDA on Mac OS X. Fix CUDA in conjunction with mpifake.