Fix some build issues
The build fails if python points to version 3 instead of version 2 (due to the use of
import cStringIO, ... which are not compatible with python3).
When configuring with
--with-python=/usr/bin/python2 (in archlinux), the build still fails because the
$(PYTHON) variable is not used everywhere it need to be in the
Also, autoconf complains about
+= being used on an uninitialized