Changed to pay attention to the 'runtime_library_dirs' list (= 'rpath'

option in the 'build_ext' command):
  * in ccompiler.py: 'gen_lib_options()' now takes 'runtime_library_dirs'
    parameter
  * in unixccompiler.py and msvccompiler.py: now pass
    'self.runtime_library_dirs' to 'gen_lib_options()', and define
    'runtime_library_dir_option()' (although in msvccompiler.py it
    blows up with a DistutilsPlatformError right now!)