unix: Use standard return codes for main

As in the CPython manual: "Unix programs generally use 2 for
command line syntax errors and 1 for all other kind of errors"
unix: Create __bss_start and _end symbols for Mach-O targets.

It's a hack, but can't find a cleaner way to do it.
tests: create result file for test/basics/memoryerror.py .

On Mac OS "python3 test/basics/memoryerror.py" never runs out of memory, the process is frozen by the os before.
unix: Add asm statements needed to read registers with clang. Code generated by gcc 4.9.0 is unchanged (same statements, different order).

Both are inefficient, saving unmodified registers on the stack.
Fix some unused variables, and silence a clang warning about initialization override in vmentrytable.h
tests/int-long.py: Try to expose issue with recent "&" optimization.
py, unix: Add copyright for modules I worked closely on.
Merge pull request #613 from pfalcon/pauls-copyr

py, unix: Add copyright for modules I worked closely on.
Merge pull request #600 from stinos/unix-exitcode

unix: Use standard return codes for main
py: Improve mpz_and function.

This should now have correct (and optimal) behaviour.
objstr.c: Partial implementation of .rsplit().

sep=None is TODO.
unix: Add "_os" module with stat().

stat() is bad function to use using FFI, because its ABI is largely private.
To start with, Glibc .so doesn't even have "stat" symbol. Then, layout of
struct stat is too implementation-dependent. So, introduce _os to deal
with stat() and other similar cases.
objstringio: Implement io.BytesIO.

Done in generalized manner, allowing any stream class to be specified as
working with bytes.
modos: Clean 64-bit issues.
sequence: Fix yet another case of improper sequence comparison.

This time, in mp_seq_cmp_bytes(). How many more cases are still lurking?
py: Implement more complete bytes comparison handling.
objstr: startswith(): Accept optional "start" arg.
py: More const usage.
py: More mp_identity usage.
py: Fix mp_obj_t -> mp_const_obj_t for mp_obj_int_get_checked()

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>