Convert (hopefully) all comparisons to NULL

Convert (hopefully) all comparisons to NULL

Apply badzero.cocci, badnull.coci and badnull2.cocci

This should convert all cases where there's a comparison to NULL to simpler
forms. This patch applies the following transformations:

code before patch               ||code after patch
===============================================================

return a == NULL;                 return !a;

return a != NULL;                 return !!a;

func(a == NULL);                  func(!a);

func(a != NULL);                  func(!!a);

b = a == NULL;                    b = !a;

b = a != NULL;                    b = !!a;

b = a == NULL ? c : d;            b = !a ? c : d;

b = a != NULL ? c : d;            b = a ? c : d;

other cases:

a == NULL                         !a
a != NULL                         a

SVN revision: 51487