Minor cleanup of riding script commands.
- The 'checkriding()' function no longer checks for wargs and dragons, ONLY Pecos, Grand Pecos, and Gryphons (as documented). (bugreport:9024)
http://rathena.org/board/tracker/issue-9024-about-renters-from-rathenanpcremerchants/
- Replaced 'checkoption()' warg checks with 'checkwug()'.

Signed-off-by: Euphy <euphy.raliel@rathena.org>