[v3 PATCH] Fix testsuite failures caused by the patch implementing LWG 2534.

[Jonathan Wakely]

On 30/11/16 17:58 +0200, Ville Voutilainen wrote:
>    Fix testsuite failures caused by the patch implementing LWG 2534.
>    * include/std/istream (__is_convertible_to_basic_istream):
>    Change the return types of __check, introduce stream_type.
>    (operator>>(_Istream&&, _Tp&&)):
>    Use __is_convertible_to_basic_istream::stream_type as the return type.
>    * include/std/ostream (__is_convertible_to_basic_ostream):
>    Change the return types of __check, introduce stream_type.
>    (operator>>(_Ostream&&, _Tp&&)):
>    Use __is_convertible_to_basic_ostream::stream_type as the return type.

As discussed on IRC, please change "stream_type" to istream_type and
ostream_type, as appropriate, because those names are already used by
stream iterators, so users can't define them as macros.

And you could make the remove_reference happen inside the
__is_convertible_to_basic_[io]stream trait, since it's only ever used
with references, but that seems stylistic.

OK with the stream_type renaming.