Turn APPLY_TAINT_PROPER into an inline function.
Turn SIZE_TO_PSIZE and DIFF into inline functions.

Changed DIFF to DIFF_OPSLOTS to better describe what it does.  Unlikely
anything uses it outside op.c.
Turn CHECKOP into an inline function.

CHECKOP() will take ops of all types, which was presuambly why it was a macro.
Instead of making the whole function a macro, just make the type casting part a macro.
Turn CHANGE_TYPE into an inline function.

Presumably this was a macro in the anticipation of needing to take more
than one type of OP.  Turns out to be unnecessary.  Can be wrapped in
a type casting macro later if necessary, like CHECKOP().