hpx::cout should be a std::ostream

[brycelelbach]

[reported by blelbach] [Trac time Mon Oct 10 12:52:16 2011] hpx::cout (and hpx iostreams in general) should inherit from std::ostream.

[brycelelbach]

[comment by hkaiser] [Trac time Mon Oct 10 12:58:44 2011] I'd suggest to build hpx::cout on top of boost::iostreams, this usually saves a lot of hassle when it comes to implementing streams.

[hkaiser]

This also includes adding an implicit flush at termination to make sure all buffers are actually sent to the console before the application exits.

[sithhell]

Closed via merging #1154