unified image loading code a little between renderers.
support switching worldmodel in csqc. also associated bugfixes.
git-svn-id: https://svn.code.sf.net/p/fteqw/code/trunk@4758 fc73d0e0-1445-4013-8a0c-d673dee63da5
In this version: replacement GL backend. Replacement D3D backend sharing code with GL. Lots of code reorganisation.
git-svn-id: https://svn.code.sf.net/p/fteqw/code/branches/wip@3401 fc73d0e0-1445-4013-8a0c-d673dee63da5