Added DeleteAndClear method to TDeletingArray.

- Normally, TDeletingArray only deletes its contents when it is destroyed.
  Now you can do it earlier if you want.
Stop leaking function damage expressions.

- Function damage expressions parsed from DECORATE are now stored in a
  single array and deleted at the end of FinishThingdef().
Better disassembly of FLOP instructions.

- Annotate FLOP instructions with the name of the floating point operation
  indicated by the C field.