Move the check_new() test to the start of op_size(). All callers used it.

Move the check_new() test to the start of op_size(). All callers used it.

This reduces the amount of repetition in the source code. Whilst it likely will
cause one extra level of function calling at runtime (for a "seen before" OP,
as op_size() now needs to be entered), it will reduce object code size, which
will compensate. Not measured the difference, but expect it all to be dwarfed
anyway by cache misses on data reads. Maintainability wins.

Also as these are major changes, reindent all sections of op_size() which have
changed.