Move python object files to python subdirectory

Move python object files to python subdirectory

Move the object files corresponding to python/*.c to the python
subdirectory in the build tree.

Because special CFLAGS are passed just to Python compilations, this
patch also required the addition of a pattern rule to update
INTERNAL_CFLAGS for here.

ChangeLog
2017-11-27  Tom Tromey  <tom@tromey.com>

	* Makefile.in (SUBDIR_PYTHON_OBS): Redefine.
	(CONFIG_SRC_SUBDIR): Add python.
	(%.o): Remove python rule.
	(python/%.o): New rule.
	* configure: Rebuild.
	* configure.ac (CONFIG_OBS): Refer to python/python.o