Add missing newline to an error message.

MFC after:	3 days
Cleanup the definition of two structures which are
exposed to userland. Therefore no MFC.
Checking for __SAPP alone is not enough because it is emulated O_APPEND
only, so works for only special fdopen() case. Add real O_APPEND too.
Back the whole change out until I figure out how to obtain O_APPEND,
it can't be used in this field at all.