Ensure python executable runs from a windows build

* Build the libpython dll where the executable is.

* Introduced variables LIBPYTHON_LIBDIR and LIBPYTHON_ARCHIVEDIR allowing
to specify output directory associated with "libpython" target independently
of the output directory associated with python extensions.

LIBPYTHON_LIBDIR / LIBPYTHON_STATIC_LIBDIR / LIBPYTHON_ARCHIVEDIR
=====================================

* On windows:

  - LIBPYTHON_LIBDIR is set to BINDIR, it means libpython27.dll will be built
  where the executable is.

  - LIBPYTHON_ARCHIVEDIR is set to ARCHIVEDIR, it means libpython27.dll
  will be built where all the extension import libraries are. This is
  consistent with what is done in the official python windows installer.

  - LIBPYTHON_STATIC_LIBDIR is set to static-ARCHIVEDIR, it means
  "libpython27.lib" corresponding to the windows static library won't overwrite
  the import library "libpython27.lib" associated with the Dll in case
  both ENABLE_STATIC and ENABLE_SHARED are ON.

* The other platforms:

 - LIBPYTHON_LIBDIR, LIBPYTHON_STATIC_LIBDIR and LIBPYTHON_ARCHIVEDIR set
 to LIBDIR

Libpython output directory
==========================

* On all platforms:

 - set libpython archive output directory
to ${CMAKE_BINARY_DIR}/${LIBPYTHON_STATIC_ARCHIVEDIR} for "libpython-static"
to ${CMAKE_BINARY_DIR}/${LIBPYTHON_ARCHIVEDIR} for "libpython-shared"

 - change libpython runtime output directory
from "libpython_shared" to ${CMAKE_BINARY_DIR}/${LIBPYTHON_LIBDIR}

PYTHONPATH on windows
=====================

* Append the build-time reference to per-configuration output
subdirectory to the available python path option.

See http://www.cmake.org/cmake/help/v2.8.10/cmake.html#variable:CMAKE_CFG_INTDIR
Set "functool", "locale", "operator" extension as built-in on windows

Since on windows, site.py relies on these modules, setting these extensions
as built-in will allow the python executable associated with a default
python build (ENABLE_STATIC:ON) to start properly.
Explicitly enable C language.

Only a C compiler is required to build python.