* tags.h: Update tag system docs.

* tags.h: Update tag system docs.
(scm_tc3_cons_gloc): Renamed to scm_tc3_struct.  Changed all uses.
(scm_tcs_cons_gloc): Renamed to scm_tcs_struct.  Changed all uses.
(SCM_ECONSP, SCM_NECONSP): Removed.  Changed all uses to SCM_CONSP
or SCM_NCONSP, respectively.

* struct.c, struct.h, srcprop.c, procs.c, procprop.c, print.c,
objects.c. modules.c, goops.c, eval.c, debug.c: Changed all uses
of scm_tc3_cond_gloc and scm_tcs_cons_gloc.  See above.

* print.c (scm_iprin1): Remove printing of glocs.  Do not try to
tell glocs from structs.

* gc.c (scm_gc_mark, scm_gc_sweep): Remove handling of glocs.

* eval.c (scm_m_atbind): Make a list of variables, not glocs.
(scm_ceval, scm_deval): For SCM_IM_BIND, fiddle with variables
instead of with glocs.
(EVALCAR): Do not test for glocs.
(scm_lookupcar, scm_lookupcar1): Do not handle glocs in race
condition.
(scm_unmemocar): Do not handle glocs.
(scm_m_atfop): Memoize as a variable, not as a gloc.
(scm_eval_args, scm_deval_args): Do not handle glocs.
(scm_ceval, scm_deval): Likewise.

* eval.h (SCM_XEVALCAR): Do not test for glocs.
(SCM_GLOC_VAR, SCM_GLOC_VAL, SCM_GLOC_SET_VAL, SCM_GLOC_VAL_LOC):
Removed.

* debug.h, debug.c (scm_make_gloc, scm_gloc_p): Removed.

* dynwind.c (scm_swap_bindings): Likewise.
(scm_dowinds): Updated to recognize lists of variables instead of
lists of glocs.

* __scm.h (SCM_CAUTIOS, SCM_RECKLESS): Update comments.