(delete_surrounding_text): Be sure to set members

(delete_surrounding_text): Be sure to set members
preceding_text and following_text to NULL.
(shift_state): Save variable values in ic_info->vars_saved.
(preedit_commit): Don't print debug information here.  Don't
change ic_info->keys here.
(get_candidate_list): Don't ref plist.
(take_action_list): Don't unref return value of
get_candidate_list.  For undo, reset ic->produced and recover
ic_info->vars.  Be sure to set ic->candidate_list to NULL after
unref it.
(init_ic_info): Set ic_info->vars_saved.
(fini_ic_info): Unref ic_info->vars_saved.
(re_init_ic): Be sure to set ic->candidate_list to NULL after
unref it.
(filter): Be sure to set members preceding_text and following_text
to NULL.  Print debug information about produced text.  Delete
processed keys from ic_info->keys.