MSVC compatibility

Replace atomic_int with atomic<int>.
MSVC does not support atomic_int initialization via constructor.
MSVC compatibility...

Cast int to std::ifstream::pos_type to disambiguate == operator.
export dataflow debugging API from marsyas DLL
cmake: FindDirectX: use find_package_handle_standard_args()
cmake: FindDirectX: fix whitespace, cosmetic changes
cmake: actually use DirectSound include directory
cmake: reuse common build instructions for MSVC, MinGW and Cygwin
cmake: add comment to clarify purpose of preprocessor definitions