use system includes for numpy (-isystem, instead of -I)
use Wdeprecated
compile flags: Wreturn-type already in Wall
use flag Wunused

Wunused-parameter + more
use Wextra flag
fix for Wextra
fix for Wextra
turn Wunused to warning, too much pain to fix right now
mute unused-parameter warnings for now

fix later in whole codebase
for GCC 4.7: use Wno-type-limits for now

enabled by Wextra & in conjunction with  Werror