EMFILE. We treat _file as an unsigned short to double our range, with a
special case for -1 (closed). Make a note of what we should do about stdio
if we ever bump libc. We could change _file in the future compatibly to an
int by putting it in the extension space but for now we don't bother.
descriptors against -1 (as appropriate).
* add actual checks which to detect stuff that would trigger_DIAGASSERT(),
and attempt to return a sane error condition.
* knf some code
* remove some `register' decls.
the first two items result in the addition of code similar to the
following in various functions:
_DIAGASSERT(path != NULL)
#ifdef _DIAGNOSTIC
if (path == NULL) {
errno = EFAULT;
return (-1);
}
#endif
