1. I forgot to say: since I add new items to `if.. elif...elif.....` chain after testing for 'big' and 'little', this change will not slowdown current external code.
2. Well, slowdown of to_bytes() between 'big' and 'net' on my PC give about 3 percents.
3. to_bytes(2, sys.byteorder) is timed exactly as 'host'.


./python -m timeit -s 'import sys' -n 10000000 '(1234).to_bytes(2, sys.byteorder)' # iteration counter is required to stabilize results.

4. As I think, Python should also be simple and intuitive. If everyone thinks as those, who set (-1) on this issue, we will neve add .to_bytes()/.from_bytes(), since there are already TWO (!) modules to do conversion to/from bytes: `ctypes` (https://docs.python.org/3/library/ctypes.html#ctypes.BigEndianStructure) and `struct`. Answer is: it is unsuitable and not comfort for the programmer. Why not to make really good practical API ?

And also, I want to call @gvanrossum.. I'm disappointed. This change is so obvious thing, that I don't understand how to explain...