number of stack narrowing specifier pairs. The first specifier in
a pair controls inner border, the second the outer border. A
number means cut that number of frames, a procedure object means
cut until that object is found in operator position in a frame.
(scm_boot_guile_1): Added calls to scm_init_backtrace and
scm_init_stacks.
* Makefile.in: Added entries for new files: backtrace.c,
backtrace.h, stacks.c and stacks.h.