- Added A_DamageSelf.

- A_DamageSelf(int amount, name damagetype)
- Added more A_Damage functions:

- A_DamageTarget
- A_DamageTracer
-Both take a number for how much damage to deal and the damagetype to
inflict. Negative numbers means healing.
- Added FDARI's A_JumpIf CheckClass submission.

- bool CheckClass(string classname, int ptr_select = aaptr_default, bool
match_superclass = false)
- Fixed a possible uninitialized condition.

In the function R_RebuildViewInterpolation, the pointer 'iview' was not initialized when the player or its camera were NULL, hence 'iview == NULL' was garbage. Also, the function FindPastViewer does not return NULL, hence the mentioned check is not needed at all. Just return early if the player camera does not exist.