tests: Add argument to allow specifying which directories to test
msvc: Only update generated headers when there are changes

This fixes generating the headers casuing complete rebuilds,
even when the headere's content didn't really change.
py: Implement bignum '&' with negatives on lhs and rhs.

Needs proper coverage testing.  Doesn't implement -ve & -ve.
Addresses issue #611.
qemu-arm: Add port README.

Based on https://github.com/micropython/micropython/pull/630 by @errordeveloper.
Merge pull request #633 from stinos/msvc-fix-genhdr-dep

msvc: Only update generated headers when there are changes
objstr: *strip(): Fix handling of one-char subject strings.
objstr: *strip(): If nothing is stripped, don't create dup string.
py: Fix break from within a for loop.

Needed to pop the iterator object when breaking out of a for loop.  Need
also to be careful to unwind exception handler before popping iterator.

Addresses issue #635.
tests: Add test for break in for.

For #635 / 25c84643b6c4da169cdb11de54f027e3c477c301.
modsocket: Remove stale ifdef.
modsocket: Add some comments on intended usage/API design of module.
objfun: Typo fixes in comments.
unix: Add poorman's stack usage info to mem_info() dump.
unix: 64-bit cleanness.
py: Reformat few long functions argument lists for clarity.
Add a comma to make the .csv look proper in github
add methods isspace(), isalpha(), isdigit(), isupper() and islower() to str
Merge pull request #644 from kimbauters/master

add methods isspace(), isalpha(), isdigit(), isupper() and islower() to str
objstr: str_uni_istype(): Codestyle.
objstr: str_uni_istype(): Spurious whitespace on empty lines.