python,build: Reinstate prepare target.
* lang/python/Makefile.am: Fix 'prepare' target. * lang/python/setup.py.in: Use 'abs_top_builddir' instead of guessing the path.
'prepare' will prepare target at PREPAREDIR. The automake integration
will also make use of prepare target. Downstream distributors may
also make use of prepare target.
- Signed-off-by: Alon Bar-Lev <alon.barlev@gmail.com>