Commented Issue: Compiling cpprest/http_client.h with g++ -Wall results in tons of warnings [173]

Compiling any code using the SDK with "g++ -Wall" results in more than a hundred warnings. The warnings are harmless: 70 of them are `-Wunknown-pragmas` and 33 more are `-Wreorder`, but it would still be nice if it could compile without warnings out of the box.
Comments: Performed some work towards this. Added a subtask in https://casablanca.codeplex.com/workitem/253.