WkDepends and release / Debug mode

[asmodehn]

When linking libraries together, one might want to chose some dependent libraries for release mode, and some dependent libraries for debug mode.
WkDepends needs to be adapted for that purpose, somehow...
Both for make ( single config builder ) and VS ( multi-config builder ).
For exemple MSVC will break on linkage if some libraries are debug and other release ( different default libs are linked )
http://stackoverflow.com/questions/2209929/linking-different-libraries-for-debug-and-release-builds-in-cmake-on-windows