Fix link problem introduced in rev 1.18 (Jul-5-2015):

When built withOUT the preprocessor macro WITH_SDL defined, ciolib.h doesn't
include gen_defs.h (perhaps it should), so the use of FREE_AND_NULL in this
file become function calls and the symbol is not found when linking.
This is why jsexec was not included in recent daily dev builds of v3.16.