new formula for gzstream lib

Gzstream is a small C++ library, basically just a wrapper, that
provides the functionality of the zlib C-library in a C++ iostream.
removed zlib dependency

zlib is provided by mac os x
formula gzstream added test #29129

added a testformula which compiles two simple test programms
audit fix for formula gzstream

Use "#{ENV.cxx}" instead of hard-coding "g++"
gzstream: add 1.5 bottle.