We want to be able to add an @ifdef annotation to optional messages
For example, we want to compile in the smartcard messages only if
libcacard is available
python_modules/demarshal.py and marshal.py fixes for gcc 4.6.0
warning about set but unused variables. The fixes disable creating
of variables mem_size when they are not used (demarshall) and
declaring a src variable when the message doesn't use it (marshal).
You need to touch *.proto after applying this (should add a Makefile
dependency).
