Fixed Resource counting bug in AutoScratchTexture detach mechanism

Before this fix, whenever a texture was detached and reattached to the texture cache (using AST::detach) it would be double counted in the cache's # of textures and memory usage stats. This would obviously lead to trouble down the road w.r.t. purging and reallocating textures.

[bsalomon, 2012-06-27 14:58:10]

On 2012/06/27 14:52:17, robertphillips wrote:

LGTM

[robertphillips, 2012-06-27 14:59:41]

committed as r4361