(syms_of_xdisp): Change doc of max-mini-window-height.

(syms_of_xdisp): Change doc of max-mini-window-height.
(resize_mini_window): Return quickly if Vresize_mini_window is
nil.  Don't return if Vmax_mini_window_height is nil.

(Vresize_mini_window, Qgrow_only): New variables.
(syms_of_xdisp): Initialize them.
(resize_mini_window): Act according to the setting of
Vresize_mini_window.
(syms_of_xdisp): Initialize Vmenu_bar_update_hook to nil.