[Development] check, Mate!

[Gábor Lehel]

Perhaps we could use GCC's poison pragma[1] to make sure that no one
uses them? In some cases it would just be replacing one error message
with another (though perhaps a more user-friendly one), but in other
cases it would substitute an error for no error. Of course, it only
works with GCC. (TBF I haven't checked any other compilers.)

[1] http://gcc.gnu.org/onlinedocs/cpp/Pragmas.html