The 'debug' flags are insufficient

Created by: siebenkopf

When I use the debug=true option in the buildout.cfg, the only compiler option that is added is -O0. This is insufficient since:

1. the NDEBUG flag is still set. This means that C++ assertions are still disabled. To avoid this, add a -UNDEBUG compiler option.
2. the BZ_DEBUG flag is not set. This means that blitz indexes are still not checked. To add this flag, use -DBZ_DEBUG=1

In fact, to be able to select point 2 (which slows down the execution tremendously) independently (and also other compiler flags), it would be nice to have a extra cflags option in the flags.