Add new C function, IsTimer, fix some rare bugs with spell timers.

In rare cases players would end up with a $ timer for a PE/debuff, this should prevent future occurrences of those bugs and also fix any currently affected characters.

While writing this fix I was looking for an easy way to query whether the enchantment list value held a timer or not, and didn't find one so I wrote in a new IsTimer function for BlakServ. Can pass it a value (eg. IsTimer(Nth(i,1)) or IsTimer(iTime) etc. We already had IsList, IsClass and so on.

IsTimer will return 1 if it is passed a timer, 0 otherwise and 0 if passed NIL ($); currently IsList returns 1 if passed NIL. I think it should probably return 0 for NIL but will wait before I change that (and it would require checking every instance of IsList in the kod code).