Avoid quadratic behavior when computing the value of a register.

    Avoid quadratic behavior when computing the value of a register.
        * frame.c (frame_stash): New static constant.
        (frame_stash_add, frame_stash_find, frame_stash_invalidate):
        New functions.
        (get_frame_id): Minor reformatting. Add the frame to the frame stash.
        (frame_find_by_id): Search the frame stash first before walking all
        frames starting from te current_frame.
        (reinit_frame_stash): Add call to frame_stash_invalidate ();