Determines whether a creature has a skill.
The creature to check for a skill. (Default: OBJECT_SELF)
Returns TRUE if oCreature has nSkill, and nSkill is useable, otherwise FALSE.
According to the Third Edition rules, some skills (such as Persuade) are usuable by anyone even if their skill rank is negative. These skills will always return a TRUE value.
author: Tom Cassiotis, editor: Ryan Hunt, additional contributor(s): Drake Coker