C++ named requirements: UnformattedOutputFunction

A UnformattedOutputFunction is a stream output function that performs the following:

# Defect reports

DRApplied toBehavior as publishedCorrect behavior
LWG 63C++98the exception-handling policy was missingadded
LWG 160C++98the process of determining whether the exception caughtis rethrown mentioned a non-existing function exception()corrected to exceptions()
LWG 165C++98the only virtual member allowed to becalled on rdbuf() was overflow()also allowedxsputn() and sync()