python: Add a flag identifying in-tree builds.
* lang/python/helpers.c (pyme_in_tree_build): New variable. * lang/python/helpers.h (pyme_in_tree_build): New declaration. * lang/python/pyme/version.py.in (in_tree_build): New variable. * lang/python/setup.py.in: Rework macro handling, set 'IN_TREE_BUILD' as appropriate.
- Signed-off-by: Justus Winter <justus@g10code.com>