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_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 libpython21.dll
  will be built where all the extension import libraries are. This is
  consistent with what is done in the official python windows installer.

* The other platforms:

 - LIBPYTHON_LIBDIR and LIBPYTHON_ARCHIVEDIR set to LIBDIR


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

* On all platforms:

 - change libpython archive output directory
from "libpython_static" to ${CMAKE_BINARY_DIR}/${LIBPYTHON_ARCHIVEDIR}

 - 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