'RELENG_7_0_0_RELEASE'.

This commit was manufactured to restore the state of the 7.0-RELEASE image.

through mbrtowc() and wcrtomb().

through byte by byte with mbrtowc(). In the usual case (buffer is big
enough to contain the multibyte character, character does not straddle
buffer boundary) this results in only one call to mbrtowc() for each
wide character read.

to the initial state when a stream is opened or seeked upon. Use the
stream's conversion state object instead of a freshly-zeroed one in
fgetwc(), fputwc() and ungetwc().

This is only a performance improvement for now, but it would also be
required in order to support state-dependent encodings.

state-dependent encodings with locking shifts will come later if there
is demand for it.

mbstate_t object that they ignore. The zeroing is fairly expensive, and it
will never be necessary in these functions; when we support state-dependent
encodings, we will pass in a pointer to the file's mbstate_t object, and
only zero it at the time the file gets opened.

handling of multibyte sequences representing null wide characters.

and __fgetwc() which can be used when we know the file is locked.

or "POSIX", other European locales). Use __sgetc() and __sputc() where
possible to avoid a wasteful lock and unlock for each byte and to avoid
function call overhead.