MAINT-616 Fix for corrupted mipmaps. Cleanup based on code review feedback.

indra/llrender/llcubemap.cpp

indra/llrender/llgl.h

indra/llrender/llimagegl.cpp

indra/llrender/llimagegl.h

indra/llrender/llrendertarget.cpp

indra/llrender/llrendertarget.h

indra/llrender/llvertexbuffer.cpp

indra/newview/app_settings/settings.xml

...view/app_settings/shaders/class1/transform/binormalV.glsl

indra/newview/llfloatermodelpreview.cpp

indra/newview/llfloatermodelpreview.h

indra/newview/llvoavatar.cpp

indra/newview/llvoavatarself.cpp

indra/newview/pipeline.cpp