GL_APPLE_object_purgeable
http://www.opengl.org/registry/specs/gl/APPLE/object_purgeable.txt
GL_APPLE_object_purgeable
	GL_BUFFER_OBJECT_APPLE 0x85B3
	GL_RELEASED_APPLE 0x8A19
	GL_VOLATILE_APPLE 0x8A1A
	GL_RETAINED_APPLE 0x8A1B
	GL_UNDEFINED_APPLE 0x8A1C
	GL_PURGEABLE_APPLE 0x8A1D
	void glGetObjectParameterivAPPLE (GLenum objectType, GLuint name, GLenum pname, GLint* params)
	GLenum glObjectPurgeableAPPLE (GLenum objectType, GLuint name, GLenum option)
	GLenum glObjectUnpurgeableAPPLE (GLenum objectType, GLuint name, GLenum option)