| This function checks all the memory for cyclic structures such | |
| as arrays containing themselves and frees them if approperiate. | |
| It also frees up destructed objects. It then returns how many | |
| arrays/objects/programs/etc. it managed | to free by doing this. |
| Normally there is no need to call this function since Pike will | |
| call it by itself every now and then. (Pike will try to predict | |
| when 20% of all arrays/object/programs in memory is 'garbage' | |
| and call this routine then.) |