Fixed compiler errors in rd-vanilla SP project.
Fixed rd-vanilla SP project for FinalBuild build configuration (I swear I
fixed it last time!)
Fixed #282 - SP and MP now use libpng instead of relying on hand-rolled
implementations. Also moved common dependencies into the lib/ folder. As a
result, had to tweak a lot of files!
Fixed SP project files for moved dependencies.
Unused variable in SV_ConSay_f
Remove old/wrong license header from sys_loadlib.h.
Will be replaced in a coming commit with correct global license.