CPython 3.6 has a few changes that, when run on uPy's test suite, give a
different output to CPython 3.5.  uPy currently officially supports the
3.4 language definition, but it's useful to be able to run the test suite
with 3.4/3.5/3.6 versions of CPython.  This patch makes such changes to
support 3.6.

The commit d9047d3c introduced a bug
whereby "from a.b import c" stopped working for frozen packages.  This is
because the path was not properly truncated and became "a//b".  Such a
path resolves correctly for a "real" filesystem, but not for a search in
the list of frozen modules.

Prints NWP/MAC/PHY version, as affected by servicepack installed.

set isn't the most basic type and can be disabled by a port.

There is no longer space reserved by default for native code.

This effectively reverts the change that introduced this new constant.
The reason is so that users do not need to rebuild the filesystem on
their modules when upgrading the firmware.

Users can change RESERVED_SECS by hand if they need the feature, and in
future firmware it may default to a non-zero value.

This code is no longer pertinent for some time - since switchover to
SDK2.0, there must be correct flash size set for bootloader, or there's
a risk of flash data corruption. And indeed, the correct flash size is
by default auto-detected by esptool.py 1.2.

With caching of map lookups in the bytecode, frozen bytecode can still
work but must be stored in RAM, not ROM.  This patch allows mpy-tool.py to
generate code that works with this optimisation, but it's not recommended
to use it on embedded targets (because of lack of RAM).

So that ports can pass their own custom options to mpy-cross.

If sets are not enabled, set literals lead to SyntaxError during parsing,
so it requires feature_check. Set tests are skipped based on set_*.py
pattern.

Otherwise, they serve reoccurring source of copy-paste mistakes and
breaking nanbox build.

Starting at esp.flash_user_start(), the reserved sectors are for general
purpose use, for example for native code generation.  There is currently
one sector reserved as such.

With warnings of need to close files, sockets, etc.

The driver seems to be be enabling the pullup resistor in most places, but
not this one. Making this one little change allows onewire devices to be
used with no external pullup resistor.