Check both in configure.ac (after checking if we need to rebuild
the marshalling files) and in the python script using pyparsing
(for people modifying .proto files in tarballs)

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).

Patch adds a "from __future__" import that doesn't affect newer python's but
allows python 2.5.4 to run the code (tested under scratchbox, n900 build environment)

It turns out that using base + sizeof(struct) is not a good way to
access an array at the end of a struct. For SpicePalette sizeof is 16, but
offset of ents is 12. Using this calculation in the demarshaller breaks
things badly, so now we use the actual array member.