Fix a render target bug by disabling environment mapping when doing full-scene RTT.

git-svn-id: svn://svn.icculus.org/fs2open@10959 387891d4-d844-0410-90c0-e4c51a9137d3
Trunk sync r10959.

git-svn-id: svn://svn.icculus.org/fs2open@10960 387891d4-d844-0410-90c0-e4c51a9137d3