Here's a new patch that addresses several remarks:

  o _decimal now has __floor__ and __ceil__methods.

  o libmpdec is now in a separate directory.

  o I removed the big libmpdec test suite. This is why:

     - It reduces the number of files that has been criticized multiple times.

     - Probably I'll be the only one who will be running the test suite.

     - The test suite is still on PyPI.

     - The test suite is so large that it's a magnet for toolchain bugs.
       For example, it found a bug in suncc (acknowledged and fixed by Sun)
       and a bug in CompCert (acknowledged and fixed by Xavier Leroy).

       I'm really worried that *if* someone runs the tests and finds
       an obscure bug, I'll have to spend hours debugging something
       that might ultimately be an external bug.

  o Renamed "python" directory into "tests".

  o Test functions in mpdecimal.c are removed.

  o All files in libmpdec that aren't required for _decimal are removed.

  o Extra functionality in _decimal.c is commented out. This does not
    yet cover the FloatOperation signal, which I would like to add
    to decimal.py as well (I'll ask later on python-dev).