fix#793, close#1791, close#1793
This brings file_win32 in sync with the documentation.
Previously, the path passed to open worked if encoded in the system
codepage (which is almost never UTF-8).
Now, the path must be encoded as UTF-8, as stated in the
documentation.
Adapt file tests so that for file_win32 all paths include a unicorn
character.
* Tidying
* Increase test coverage
* Fix file_mode::append_existing
API Changes:
* file_mode::append_new is removed, as it makes no sense
Actions Required:
* Replace file_mode::append_new with file_mode::append
or file_mode::append_existing instead of file_mode::append_new
fix#1356
* File functions return errc::bad_file_descriptor
instead of errc::invalid_argument.
Actions Required:
* Callers checking for errc::invalid_argument from calls to
file APIs should check for errc::bad_file_descriptor instead.
Mika Fischer
Damian Jarek
Vinnie Falco