Create new member function release_token( ).
Reference root_token instead of token_for_context(c) after rerooting.
Introduce reroot_at_context(int c).
Add swap_tokens( ) function.
Assume that reroot_at( ) might change our parent token.
Avoid changing root token.
Actually make the root token constant.
Call check_tokens in the right place.
lazy_evaluate( ) should call incremental_evaluate_in_context( ).
Add wrapper incremental_evaluate_unchangeable( ).
Check incremental_evaluate( ) and incremental_evaluate_unchangeable( )
Check set_reg_value( ).
Fix checks for DEBUG_MACHINE >= 2
Check newly created regs if DEBUG_MACHINE >= 3
Genericize clean_weak_refs( ).