A VfsPosix created with a relative root path would get confused when
chdir() was called on it and become unable to properly resolve absolute
paths, because changing directories effectively shifted its root. The
simplest fix for that would be to say "don't do that", but since the
unit tests themselves do it, fix it by making a relative path absolute
before storing it.
Signed-off-by: Christian Walther <cwalther@gmx.ch>
Prevent handle leaks when file objects aren't closed explicitly and
fix some MICROPY_CPYTHON_COMPAT issues: this wasn't properly adhered
to because #ifdef was used so it was always on, and closing files
multiple times should be avoided unconditionally.
Christian Walther