(Fkeymap_prompt, Fcurrent_active_maps): New funs.

(Fkeymap_prompt, Fcurrent_active_maps): New funs.
(accessible_keymaps_1): New function.
(Faccessible_keymaps, accessible_keymaps_char_table): Use it.
(Fwhere_is_internal): Use Fcurrent_active_maps.
(Fdescribe_buffer_bindings): Renamed from describe_buffer_bindings.
Insert in current buffer rather than standard-output.
Don't call `help-mode'.  Export to elisp.
(describe_buffer_bindings): New wrapper.
(syms_of_keymap): Defsubr Skeymap_prompt, Scurrent_active_maps
and Sdescribe_buffer_bindings.