* dynl.c, error.c, eval.c, feature.c, filesys.c, fports.c, list.c, load.c,

* dynl.c, error.c, eval.c, feature.c, filesys.c, fports.c, list.c, load.c,
net_db.c, read.c, socket.c: Update error messages to use ~A for
%s, ~S for %S to work with new `simple-format' format and be
standardized better.

* print.h, print.c (scm_simple_format): Added `simple-format'
primitive.  It's the old scm_display_error, with ARGS now a rest
parameter, and the destination first instead of last (and a couple
new capabilities inspired by `format' -- #t as destination means
current-output-port, #f means return the formatted text as a
string.

* gh.h, gh_data.c, ports.h, ports.c: Added some missing const specifications.

* backtrace.c (scm_display_error_message): Rewrote to use
scm_simple_format() procedure.

* __scm.h: Added commented-out #define of GUILE_DEBUG_FREELIST