Enable extra gcc warnings

Author: pdp7

setup.py

@@ -18,7 +18,7 @@
 else:
     kernel41 = None
 
-CFLAGS = ['-Wall', '-Werror', '-Wno-format-security']
+CFLAGS = ['-Wall', '-Werror', '-Wextra', '-Wno-format-security']
 
 classifiers = ['Development Status :: 3 - Alpha',
                'Operating System :: POSIX :: Linux',