Refactor code copied among the r7 paths for checking incoming message types
Do the same for r3
It remains to do the same to sign r4 and r8
change zip2, zip3 to make them much more versatile---they can now handle any combination of iter and into_iter simply by borrowing or taking ownership of input args, respectively.
fix #145
Also:
zip2,zip3to make them much more versatile---they can now handle any combination ofiterandinto_itersimply by borrowing or taking ownership of input args, respectively.