cmake python config bugs fixed

Python and pybullet remain optional with these changes.
A specific python version can now be selected by setting PYTHON_VERSION_PYBULLET.
The python library version must now match the interpreter version exactly.
If all required python dependencies are found, pybullet is now enabled by default.
Changes incorporate the following BSD licensed cmake code:
32bf5c7ad8/CMakeScripts/FindNumPy.cmake
https://github.com/NikolausDemmel/CMake/pull/2/files
86578eccf2/Modules/SelectLibraryConfigurations.cmake

build3/cmake/FindLibPython.py

@@ -0,0 +1,25 @@
+# Note by Nikolaus Demmel 28.03.2014: My contributions are licensend under the
+# same as CMake (BSD). My adaptations are in part based
+# https://github.com/qgis/QGIS/tree/master/cmake which has the following
+# copyright note:
+
+# FindLibPython.py
+# Copyright (c) 2007, Simon Edwards <simon@simonzone.com>
+# Redistribution and use is allowed according to the terms of the BSD license.
+# For details see the accompanying COPYING-CMAKE-SCRIPTS file.
+
+import sys
+import distutils.sysconfig
+
+print("exec_prefix:%s" % sys.exec_prefix)
+print("major_version:%s" % str(sys.version_info[0]))
+print("minor_version:%s" % str(sys.version_info[1]))
+print("patch_version:%s" % str(sys.version_info[2]))
+print("short_version:%s" % '.'.join(map(lambda x:str(x), sys.version_info[0:2])))
+print("long_version:%s" % '.'.join(map(lambda x:str(x), sys.version_info[0:3])))
+print("py_inc_dir:%s" % distutils.sysconfig.get_python_inc())
+print("site_packages_dir:%s" % distutils.sysconfig.get_python_lib(plat_specific=1))
+for e in distutils.sysconfig.get_config_vars ('LIBDIR'):
+    if e != None:
+        print("py_lib_dir:%s" % e)
+        break