chaining the live guardians in a single-linked list during the GC
mark phase.
(GUARDIAN_NEXT): convenience macro to access the `next' field.
(guardians, guardians_size, n_guardians): deleted.
(first_live_guardian, current_link_field): new globals used to
point to the head of the live guardian list and current `next'
field, respectively.
(g_mark): append the guardian to the live guardian list.
(scm_guardian_gc_init): zero the live guardian list.
(scm_guardian_zombify): iterate through the live guardian list.
scm_guardian_gc_init, scm_guardian_zombify, scm_guard,
scm_get_one_zombie, scm_init_guardian): This is an implementation
of guardians as described in R. Kent Dybvig, Carl Bruggeman, and
David Eby (1993) "Guardians in a Generation-Based Garbage
Collector" ACM SIGPLAN Conference on Programming Language Design
and Implementation, June 1993 ftp://ftp.cs.indiana.edu
/pub/scheme-repository/doc/pubs/guardians.ps.gz
Author: Michael N. Livshin.
