[GH #911] Provide strerror for unknown filehandle errors

Unify printed type: filehandle => FileHandle, to sync with generic Parrot_io_open
"Cannot open %s, no path", vtable->name errmsg.
Merge branch 'rurban/fh-strerr-gh911'
Add ChangeLog for GH #911: Add OS error messages to FileHandle.open() error messages