* gc-segment.c (scm_i_make_initial_segment): check user settings

* gc-segment.c (scm_i_make_initial_segment): check user settings
for sanity.

* gc-malloc.c (scm_gc_init_malloc): check user settings for
sanity.
(scm_gc_register_collectable_memory): prevent overflow of memory
counts.

* gc-freelist.c (scm_init_freelist): check user settings for sanity.

* gc-malloc.c (scm_gc_register_collectable_memory): use floats;
these won't ever wrap around with high memory usage.

* gc-freelist.c: include <stdio.h>

* gc-malloc.c: add DEBUGINFO for mtrigger GCs.