xterm.c (x_clear_frame) - commented out call to XClearWindow

[Geoff Gole <geoffgole@gmail.com>]

In x_clear_frame in in xterm.c, somebody has commented out a call to
XClearWindow:

  /* The following call is commented out because it does not seem to accomplish
     anything, apart from causing flickering during window resize.  */
  /* XClearWindow (FRAME_X_DISPLAY (f), FRAME_X_WINDOW (f)); */

Unfortunately this results in a strip of pixels at the bottom of the
frame not being updated. You might be able to see it with:

  emacs -Q
  M-: (set-background-color "black")

Uncommenting the call fixes the problem, but results in the
aforementioned flicker during resize. Can we instead update only the
problematic strip:

  {
    int covered_pixels = FRAME_TEXT_LINES_TO_PIXEL_HEIGHT (f, FRAME_LINES (f));
    int leftover_pixels = FRAME_PIXEL_HEIGHT (f) - covered_pixels;

    XClearArea(FRAME_X_DISPLAY (f), FRAME_X_WINDOW (f),
               0, FRAME_PIXEL_HEIGHT (f) - leftover_pixels,
               FRAME_PIXEL_WIDTH (f), leftover_pixels,
               0);
  }

Do I have this right? (I'm not familiar with either frame.c or xterm.c.)