python: Use one copy of the source tree per Python version.
* lang/python/Makefile.am (copystamp): Create one copy per Python version. (all-local): Adapt. (clean-local): Likewise. (install-exec-local): Likewise. * lang/python/tests/run-tests.py: Likewise.
Currently, we use one copy of the Python module's source to build for
all Python versions. This is problematic, because SWIG writes a
wrapper file into the source tree. Currently, this file works with
both Python 2 and 3, but this is purely by chance.
Improve the situation by creating one copy per Python version so that
SWIG can write version-specific code into each copy.
- Signed-off-by: Justus Winter <justus@g10code.com>