scm_is_false instead of == SCM_BOOL_F; also is_null, is_true, etc

scm_is_false instead of == SCM_BOOL_F; also is_null, is_true, etc

* libguile/deprecation.c (scm_issue_deprecation_warning)
* libguile/eval.c (CAPTURE_ENV):
* libguile/goops.c (make_dispatch_procedure, make_class_from_symbol):
  (create_smob_classes):
* libguile/guardians.c (finalize_guarded, scm_i_get_one_zombie):
* libguile/hashtab.c (scm_fixup_weak_alist, scm_internal_hash_fold):
* libguile/i18n.c (scm_nl_langinfo)
* libguile/load.c (scm_primitive_load)
* libguile/posix.c (scm_setrlimit)
* libguile/socket.c (scm_to_sockaddr):
* libguile/srcprop.c (scm_make_srcprops): Use scm_is_false / scm_is_true
  / scm_is_null instead of comparing against SCM_BOOL_F et al.