Make pyboard.enter_raw_repl more robust

In case there's a program in the microcontroller's main.py running in an infinite loop
Fix pyboard.py tests.
Fix PB0 ADC typo.

This also adds a bunch of slashes separating pin that have multiple functions.
Add device ID to autoflash script.
Merge pull request #547 from cjbarnes18/pyboard_module_fixes

Fix pyboard.py tests.
Merge pull request #549 from cjbarnes18/autoflash_device

Add device ID to autoflash script.
Merge pull request #548 from dhylands/fix-pin-defn

Fix PB0 ADC typo.
py: Use <alloca.h> for alloca()

alloca() is declared in alloca.h which als happens to be included by stdlib.h.
On mingw however it resides in malloc.h only.
So if we include alloca.h directly, and add an alloca.h for mingw in it's port
directory we can get rid of the mingw-specific define to include malloc.h
and the other ports are happy as well.
Ignore .exe files
More relaxed parsing of preprocessed qstr header

The original parsing would error out on any C declarations that are not typedefs
or extern variables. This limits what can go in mpconfig.h and mpconfigport.h,
as they are included in qstr.h. For instance even a function declaration would be
rejected and including system headers is a complete no-go.
That seems too limiting for a global config header, so makeqstrdata now
ignores everything that does not match a qstr definition.
mingw: Add 'open' as extra builtin and add define MICROPY_MOD_SYS_STDFILES

This one was probable missed when creating mpconfigport.h, but the underlying
code (file.c) gets compiled and works perfectly so no reason to omit it.
objclosure, objcell: Print detailed representation if was requested.

Well, it is bound to "detailed error reporting", but that's closest what we
have now without creating new entities.
Merge pull request #553 from stinos/ignore-exe

Ignore .exe files
Merge pull request #550 from stinos/mingw-open

mingw: Add 'open' as extra builtin
Merge pull request #552 from stinos/mingw-alloca

py: Use <alloca.h> for alloca()
stmhal: Add documentation for RTC class.
windows: alloca.h: Add comment, fix line endings.
Merge branch 'master' of github.com:micropython/micropython
stmhal: Add example use to RTC doc; add rtc.c to gendoc.py.
CPython compatibility: raise an error for operations on a closed file descriptor

In CPython any operations on a file that has been closed already reaises
a ValueError with message "I/O operation on closed file"