Reworked v_isometric code significantly, it now defaults to a proper isometric view...

Reworked v_isometric code significantly, it now defaults to a proper isometric view and some maps are actually playable like this.

Added R_Viewport_InitOrtho3D which more correctly implements the VF_PERSPECTIVE=0 case for CSQC, with correct camera orientation and all that.  This may break existing mods that tried to use that feature but I doubt there are any as it was pretty broken before.

Reworked how R_CanSeeBox (and other vis code) determine if the view is able to use vieworigin based culling or not, this is now a separate property (r_refdef.view.usevieworiginculling) and can be turned on or off for reflection views and such.  This is also exposed as v_isometric_usevieworiginculling for the v_isometric case.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12398 d7cf8633-e32d-0410-b094-e92efae38249