Finished the overhaul of byte-compilation options: there's now a 6-way

Finished the overhaul of byte-compilation options: there's now a 6-way
choice between (compile, no-compile) * (optimize=0, optimize=1,
optimize=2).  Details:
  - added --no-compile option to complement --compile, which has
    been there for ages
  - changed --optimize (which never worked) to a value option, which
    expects 0, 1, or 2
  - renamed 'bytecompile()' method to 'byte_compile()', and beefed
    it up to handle both 'compile' and 'optimize' options
  - fix '_bytecode_filenames()' to respect the new options