texture caching fixes

[James W. W. <ja...@fr...>]

I just made some changes to the way the interactive renderer caches 
textures.  Here's why:  We were caching the texture object, but 
invalidating it if either the texture object or the texture shader 
had a change in edit index.  This meant that if your scene contained 
two texture shaders using the same texture object, and the shaders 
happened to have different edit index, then the texture cache would 
always be invalid and the texture would be reloaded on every frame. 
Also, if the two shaders had different UV transforms, then that 
difference would not be maintained.
-- 
   James W. Walker, ScriptPerfection Enterprises, Inc.
   <http://www.write-brain.com/>