Allow python to find its files if moved from original location.

	Allow python to find its files if moved from original location.
	* acinclude.m4 (GDB_AC_DEFINE_RELOCATABLE): New function.
	(GDB_AC_WITH_DIR): Call it.
	* configure.ac: Define WITH_PYTHON_PATH if we can find the
	python installation directory.
	* config.in: Regenerate.
	* configure: Regenerate.
	* defs.h (python_libdir): Declare.
	* main.c (python_libdir): Define.
	(captured_main): Initialize python_libdir.
	* python/python.c (_initialize_python): #ifdef WITH_PYTHON_PATH,
	call Py_SetProgramName to make sure python can find its libraries
	and modules.