Custom URL handlers for the vgui::HTML panel now pass the URL and protocol and changed VBSP to check both the EXECUTABLE_PATH and the MOD path for FDG files.

Custom URL handlers for the vgui::HTML panel now pass the URL and protocol and changed VBSP to check both the EXECUTABLE_PATH and the MOD path for FDG files. See https://github.com/ValveSoftware/source-sdk-2013/pull/116 and https://github.com/ValveSoftware/source-sdk-2013/pull/146.