(make_window): Initialize resize_proportionally.

(make_window): Initialize resize_proportionally.
(enlarge_window): Temporarily set resize_proportionally to make
sure that shrink_windows does scale the window proportionally.
(shrink_windows): When window has resize_proportionally set try
to shrink it proportionally by stealing from other windows.
(struct saved_window, Fset_window_configuration)
(compare_window_configurations): Handle resize_proportionally.
(WINDOW_TOTAL_SIZE): New macro.
(window_min_size, shrink_windows, size_window): Use it.
(check_min_window_sizes): Removed.  Invalid values of
window-min-height|width are handled by window_min_size_2 now.
(size_window, Fsplit_window, enlarge_window)
(adjust_window_trailing_edge, grow_mini_window): Don't call
check_min_window_sizes.
(window_min_size_2, window_min_size_1, window_min_size): New
argument safe_p for retrieving "safe" minimum sizes.
(Fdisplay_buffer, Fsplit_window, enlarge_window):
(adjust_window_trailing_edge, grow_mini_window): Adjust
arguments of window_min_size... functions.
(shrink_windows): Argument min_size removed.  New argument
safe_p allows shrinking windows to their safe minimum sizes.
Calculate minimum size and decide whether a window shall be
deleted for each window individually.
(size_window): When nodelete_p equals 2, tell shrink_windows to
delete windows only if their new minimum size is no more safe.
(shrink_window_lowest_first): Call window_min_size_1 to make
sure to preserve modeline of bottom-most window when resizing
the minibuffer.
(Fset_window_configuration, Fcurrent_window_configuration)
(compare_window_configurations): Do not handle
window-min-height|width any more.
(syms_of_window): Clarify window-min-height|width doc-strings.