* options.c (protected_objects, scm_init_options): The content of

* options.c (protected_objects, scm_init_options):  The content of
protected_objects is now protected from garbage collection using
scm_gc_register_root instead of scm_permanent_object.

(get_option_setting):  New static function that	computes an option
setting as it was formerly done in the function scm_options.

(get_documented_option_setting):  New static function that
returns option documentation as it was formerly done in the
function scm_options.  Note that documentation C strings are no
longer precomputed into SCM objects.  Instead, they are converted
into SCM strings every time get_documented_option_setting is
called.

(change_option_setting):  New static functions that modifies the
option setting as it was formerly done in the function
scm_options.  The function is now exception safe, i. e. won't
cause a memory leak when interrupted.  Further, only non-immediate
option values are added to the protection list.

(scm_options):  This function now has only the purpose to dispatch
to to get_option_setting, get_documented_option_setting or
change_option_setting, depending on the arguments given to
scm_options.

(scm_init_opts):  Don't convert documentation C strings into SCM
strings.  Further, don't protect any object values:  They _must_
be immediate values, otherwise there is no guarantee that they
have not been collected before anyway.

* options.[ch] (scm_t_option):  Made type unsigned, name into a
constant char* and val into a scm_t_bits type.

(scm_options, scm_init_opts):  The number of options is guaranteed
to be larger or equal to zero.  Thus, the type is changed to
unsigned.