This makes int.from_bytes() work for MICROPY_LONGINT_IMPL_LONGLONG.

These short unit tests test the base uPy methods as well as parts of the
websocket protocol, as implemented by uPy.

@dpgeorge converted the original socket based tests by @hosaka to ones
that only require io.BytesIO.

This test just tests that the basic functions/methods can be called with
the appropriate arguments.  There is no real test of underlying
functionality.

Thanks to @hosaka for the initial implementation of this test.

Two independent fixes:
- need to prefix symbols referenced from asm with underscore;
- need to undo the C-function prelude.

Mostly intended to ease experimentation, no particular plans for APIs
so far (far less their stability), is_preempt_thread() provided is
mostly an example.

Actually, this removes -fno-omit-frame-pointer workaround for Zephyr.

By adding back monotonically increasing field in addition to time field.
As heapsort is not stable, without this, among entried added and readded
at the same time instant, some might be always selected, and some might
never be selected, leading to scheduling starvation.

esptool 1.3 now supports both Python 2.7 and 3.4+.
Updated github link to now-official espressif repo.

*a, = b should always make a copy of b, instead, before this patch
if b was a list it would copy only a reference to it.

I.e. they don't run successfully with MICROPY_LONGINT_IMPL_NONE
and MICROPY_LONGINT_IMPL_LONGLONG (the problem is that they generate
different output than CPython, TODO to fix that).

The use of large literal numbers is a big no-no when it comes to writing
programs which work with different int representations. Also, some checks
are pretty adhoc (e.g using struct module to check for 64-bitness). This
change bases entire detection on sys.maxsize and integer operarions, and
thus more correct, even if longer.

Note that this change doesn't mean that any of these tests can pass with
anything but MPZ - even despite checking for various int representations,
the tests aren't written to be portable among them.

INT_MAX used previosly is indeed max value for int, whereas on LP64
platforms, long is used for mp_int_t. Using MP_SMALL_INT_MAX is the
correct way to do it anyway.

nlr_jump is a little bit inefficient because it now saves a register to
the stack.

Each threads needs to have its own private references to its current
locals/globals dicts, otherwise functions running within different
contexts (eg imported from different files) can behave very strangely.

TODO: There's another issue to care about: poll set being modified during
iteration.

Tests which don't work with small ints are suffixed with _intbig.py. Some
of these may still work with long long ints and need to be reclassified
later.

Big aka arbitrary-precision integers (implemented by MPZ module) are used
in tests starting with "int_big_" or ending with "_intbig".