GL_NV_depth_buffer_float
http://developer.download.nvidia.com/opengl/specs/GL_NV_depth_buffer_float.txt
	GL_DEPTH_COMPONENT32F_NV 0x8DAB
	GL_DEPTH32F_STENCIL8_NV 0x8DAC
	GL_FLOAT_32_UNSIGNED_INT_24_8_REV_NV 0x8DAD
	GL_DEPTH_BUFFER_FLOAT_MODE_NV 0x8DAF
	void glDepthRangedNV (GLdouble zNear, GLdouble zFar)
	void glClearDepthdNV (GLdouble depth)
	void glDepthBoundsdNV (GLdouble zmin, GLdouble zmax)