change #include for relative path in .hpp files
fixed opentxs.pc.in since updated headers
fix for NULL in OTAsymmetricKey.hpp
change <ot_config.h> to ot_config.h
change <ot_config.h> to ot_config.h in stdafx.h
make irrXML.hpp included relatively in .hpp files
make zmq optional for header only compile
Merge pull request #46 from da2ce7/master

Fixes needed for Moneychanger.  Discovered in: https://github.com/Open-Transactions/Moneychanger/pull/67
tighten up disabled warning for windows
bump version to 0.91.a
Merge pull request #47 from da2ce7/master

Bump Version to 0.91.a (inc. some build mods for windows).