Fix compilation with gcc 4.3 and glibc 2.8.90.

Fix compilation with gcc 4.3 and glibc 2.8.90.

src/mod-helpserv.c (create_request): Use explicit format strings for
  sprintf() when no format argument is passed.
src/modcmd.c: Store the result of strtoul() into a variable.
src/nickserv.c: Pay attention to the return value of fgets().