(keymap_parent): New fun, extracted from Fkeymap_parent.

(keymap_parent): New fun, extracted from Fkeymap_parent.
(Fkeymap_parent, keymap_memberp, fix_submap_inheritance): Use it.
(Fset_keymap_parent): Gcpro a bit more.
(access_keymap): Gcpro around meta_map call and around the main loop.
(get_keyelt): Gcpro when following indirect references.
(copy_keymap_item): New fun, extracted from Fcopy_keymap.
(copy_keymap_1, Fcopy_keymap): Use it.  Don't copy the parent map.
(Fdefine_key, Flookup_key): Gcpro before calling get_keymap.
Remove useless ad-hoc remap code.