Improve handling of list mode limits.•••- Fix not being able to set a zero limit.
- Fix MAXLIST not reflecting the true lower limit.
- Fix not treating an empty <maxlist:limit> as equivalent to *.
Re-order the includes to fix C++03 builds.•••inspircd.h defines __STDC_LIMIT_MACROS to ensure that C99 int type
limits are defined, however, if <stdint.h> is included implicitly
before inspircd.h, the build fails due to the C99 integer type
limits being undefined.