More violent warning about using NO_TAINT_SUPPORT

More violent warning about using NO_TAINT_SUPPORT

I failed to update the commit message of the previous commit (sorry!).
The code is in a much better shape than the message claims and Configure
support, for example, won't be added at all to require more
determination from users. PL_taint_warn has since received the same
treatment. To wit:

 #   define TAINT_WARN_get       (PL_taint_warn)
 #   define TAINT_WARN_set(s)    (PL_taint_warn = (s))