misc improvements to hybrid collector

Including:
- Deprecated dated test cases.
- Reduced root set scanning frequency on old generation.
- Objects are allocated as white on old generation.
- When redirection table is full, pointers are forwarded.
- Eliminated dirty words on young generation.

Next:
How not to scanning root set and young generation for every
copy/alloc operation? The current situation is, if not, newly
copy/allocated live objects are not traced, and will be freed.