Doxygen: Updated path to libdeng1 sources
Merge branch 'master' of ssh://github.com/skyjake/Doomsday-Engine
Fixed: Build failures

Usage of extern "C", missing //, and missing import of the Map API in
wadmapconverter.
Fixed|Windows: Build failure

Shuffled header includes in p_dmu.cpp to get around fragile Windows
system headers.