[v3] support mixing std::bind and tr1::bind

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

This allows std::bind and tr1::bind to work together and support each
other's placeholders and recognise each other's call wrappers as bind
expressions.

        * include/std/functional (is_placeholder, is_bind_expression): Add
        partial specializations for cv-qualified types.
        * include/tr1/functional (is_placeholder, is_bind_expression): Add
        partial specializations for std::bind and std::placeholders and for
        cv-qualified types.
        * testsuite/20_util/bind/cv_quals_3.cc: New.
        * testsuite/tr1/3_function_objects/bind/cv_quals.cc: New.
        * testsuite/tr1/3_function_objects/bind/mixed.cc: New.

Tested x86_64-linux, committed to trunk.

Attachment: bind.txt
Description: Text document