some fixes to return values of reverse_iterator methods, and addition of reverse_iterator operators
created as a first stab at solving some implementation problems... see upcoming commits
Implemented tests for remaining methods, and fixes resulting from them.

These include a fix to a similar problem encountered with vectors, where type inference results in calling the wrong insert method.
The new dstd.hxx file, is used in a first attempt at a solution to this.
I based that solution on what the gcc stl seems to do.