(r_re_alloc): Correct realloc behavior--allow shrinking

(r_re_alloc): Correct realloc behavior--allow shrinking
of blocks while reallocating, if shrinking by more than one page.
(relocate_blocs, resize_blocs): Added failsafe to protect future
calling of these routines when in frozen state.
(r_alloc_thaw): Added call to r_alloc_init.
(relocate_blocks, resize_bloc, r_alloc_sbrk, r_alloc_thaw): Extended
functionality to let ralloc package work in frozen state, allowing
for the existence of unused blocks.