* non-Windows dstream is a simple reference alias
* dstream constructor takes a target ostream argument
* dstream inherits the unitbuf setting of the target stream
The log member is changed to derive from std::ostream. A new
class dstream is derived from std::ostream to support redirection
to the Visual Studio Output Window if a debugger is attached.
Obsolete classes abstract_ostream and its derived variants are
removed.
Nik Bougalis
Vinnie Falco