// For each program, a list of other programs that are exactly like it.
// By default, will only contain the program itself, but due to cloning
// (see use_glsl_program()), may grow. Programs are taken off this list
// while they are in use (by use_glsl_program()).
// For each program, a list of other programs that are exactly like it.
// By default, will only contain the program itself, but due to cloning
// (see use_glsl_program()), may grow. Programs are taken off this list
// while they are in use (by use_glsl_program()).