Add support for the send/recvmsg API to the socket module. Patch by David Watson and Heiko Wundram. (Closes #6560)

Patch by Jeremy Kloth.

I need this to fix the failing test_command_install_dist.

I need this to fix the failing test_install.

sched_setparam() returning EINVAL for processes with SCHED_OTHER scheduling
policy.

 * Use str.startswith(tuple): I didn't know this Python feature, Python rocks!
 * Replace sometimes sys.platform.startswith('linux') with
   sys.platform == 'linux'
 * sys.platform doesn't contain the major version on Cygwin on Mac OS X
   (it's just 'cygwin' and 'darwin')

Copy/paste (from Python 3.2) failure

On Linux, sys.platform doesn't contain the major version anymore. It is now
always 'linux', instead of 'linux2' or 'linux3' depending on the Linux version
used to build Python.

same object as reader and writer, and deemphasize it in document order.

same object as reader and writer, and deemphasize it in document order.

could appear on BufferedRandom streams.

could appear on BufferedRandom streams.

Even if Python is compiled on Linux 3.