Blender Git Loki

* Made options evaluate differently, so setting one option properly
propagates to related options:

In (platform)-config.py
BF_PYTHON_VERSION = '2.4'
BF_PYTHON_INC = '/usr/include/python${BF_PYTHON_VERSION}'

In user-config.py
BF_PYTHON_VERSION = '2.3'

This will now have BF_PYTHON_INC evaluate actually to
'/usr/include/python2.3' and not to '/usr/include/python2.4' as with
the old way. Reported by Chris Want.

Todo: also use in other platform configurations.