unix: Properly recognize and report when script on cmdline not found.

Previosuly just silently exited.
unix: Support #if-able impl-specific cmdline options.

For example, we still build w/o GC enabled, so cannot really set heap size.
unix: Use argv[0] for command name in usage.
gc: Uses uint defined in misc.h.
tests/string-format: Add test for formatting ints with float format.

Fail currently.
unix: Enable GC.

GC support for "unix" port was implemented some time ago, but still not
enabled.
stmhal: Fix servo object; add fpclassify to math functions.
Merge branch 'master' of github.com:micropython/micropython
py: Fix regress for printing of floats and #if.

Also change formating modifier in test script (it still passes with
original format though).
Fix str.format to work with {:f/g/e} and ints

Also fix objstr.c to compile when floats disabled.
Merge branch 'fix-format-int' of github.com:dhylands/micropython into dhylands-fix-format-int

Conflicts:
	py/objstr.c
Merge pull request #417 from pfalcon/unix-enable-gc

unix: Enable GC.
py: More robust int conversion and overflow checking.
py: Add "io" module.

So far just includes "open" function, which should be supplied by a port.

TODO: Make the module #ifdef'ed.
unix file: Implement context manager protocol (for "with" statement).
run-tests: Allow to override python3 command to use via environment var.
stmhal: Reimplement file support using stream protocol API.

This adds readline(), readall(), etc. methods. Also other fixes to make
Python API compliant and "with" support.
README: ARM Linux is supported.

Retested again on Ubuntu 12.04 armhf running in chroot on Samsung
ARM Chromebook (Cortex-A15).
stmhal: #undef log2f if it's defined.
stmhal: Add powf, logf, log2f, log10f.