drop the lame ADD_*_CPPFLAGS and FORCE_*_LDFLAGS for the less weird PKG_*_CPPFLAGS and PKG_*_LDFLAGS. Also, in the process, fix an annoying bug where setting PKG_FOO_CPPFLAGS (where FOO can be fulfilled by BAR and BAZ) wouldn't be propagated to PKG_BAR_CPPFLAGS. This way, people don't have to know which of the alternatives to pass in CPPFLAGS/LDFLAGS for.
… This will slow down the NURBS considerably, but produce much smoother results for the Apollo dataset.
Moved config.options.default to config.options.irg. Created a config.options.example that is more generic.