- Use absolute imports
- Fix StringIO import so that 2to3 can translate it

(as submitted here https://bugs.launchpad.net/pycrypto/+bug/544792)
so that they are available also in Python 2.1, 2.2, 2.3 and 2.4.

Regardless where the implementation comes from (Python standard
library or our native modules, depending on the Python version),
all Crypto.Hash objects are always used as front-ends.

Doing the wraping later, at the point of use instead.

o _fastmath now builds and runs on PY3K
o Changes to setup.py to allow /usr/include for gmp.h
o Changes to setup.py to allow linking fastmath w/ static mpir
  on Windows without warning messages
o Changes to test_DSA/test_RSA to throw an exception if _fastmath
  is present but cannot be imported (due to an issue building
  _fastmath or the shared gmp/mpir libraries not being reachable)
o number.py has the code to flag a failing _fastmath, but that
  code is commented out for a better runtime experience
o Clean up the if for py21compat import - should have been == not is
o Clean up some '== None' occurences, now 'is None' instead

In an attempt to simplify the copyright status of PyCrypto, I'm placing my
code into the public domain, and encouraging other contributors to do the
same.

I have used a public domain dedication that was recommended in a book on FOSS legal
issues[1], followed by the warranty disclaimer boilerplate from the MIT license.

[1] _Intellectual Property and Open Source: A Practical Guide to Protecting
    Code_, a book written by Van Lindberg and published by O'Reilly Media.
    (ISBN 978-0-596-51796-0)

This will avoid the previous situation where scripts like the old "test.py"
get included accidentally in a release.  It also frees us to put additional
build scripts in the top-level directory of the source tree.