Omit module functions when there's no code

MSHUTDOWN, RINIT, RSHUTDOWN and MINFO are often empty, so check and
omit them if this is the case, and set the module structure entry to
NULL instead.  Reduces code size, number of external functions on the
module, and runtime overhead a little (RINIT and RSHUTDOWN are called
on every request when used with a webserver).
1 file changed