Revert "x11: drop xscrnsaver use"

This broke screensaver/powersave inhibition with at least KDE and
LXDE. This is a release blocker.

Since fdo, KDE and GNOME idiots seem to be unable to reach
a consensus on a simple protocol, this seems unlikely to get
fixed upstream this year, so revert this change.

Fixes #4752.
Breaks #4706 but I don’t give a damn.

This reverts commit 3f75b3c343.

README.md

@@ -96,7 +96,7 @@ Example:
 Essential dependencies (incomplete list):
 
 - gcc or clang
-- X development headers (xlib, xrandr, xext, xinerama, libvdpau,
+- X development headers (xlib, xrandr, xext, xscrnsaver, xinerama, libvdpau,
   libGL, GLX, EGL, xv, ...)
 - Audio output development headers (libasound/ALSA, pulseaudio)
 - FFmpeg libraries (libavutil libavcodec libavformat libswscale libavfilter

video/out/x11_common.c

@@ -33,6 +33,7 @@
 #include <X11/XKBlib.h>
 #include <X11/XF86keysym.h>
 
+#include <X11/extensions/scrnsaver.h>
 #include <X11/extensions/dpms.h>
 #include <X11/extensions/Xinerama.h>
 #include <X11/extensions/Xrandr.h>
@@ -1907,9 +1908,22 @@ static void xscreensaver_heartbeat(struct vo_x11_state *x11)
     {
         x11->screensaver_time_last = time;
         sem_post(&x11->screensaver_sem);
+        XResetScreenSaver(x11->display);
     }
 }
 
+static int xss_suspend(Display *mDisplay, Bool suspend)
+{
+    int event, error, major, minor;
+    if (XScreenSaverQueryExtension(mDisplay, &event, &error) != True ||
+        XScreenSaverQueryVersion(mDisplay, &major, &minor) != True)
+        return 0;
+    if (major < 1 || (major == 1 && minor < 1))
+        return 0;
+    XScreenSaverSuspend(mDisplay, suspend);
+    return 1;
+}
+
 static void set_screensaver(struct vo_x11_state *x11, bool enabled)
 {
     Display *mDisplay = x11->display;
@@ -1917,6 +1931,8 @@ static void set_screensaver(struct vo_x11_state *x11, bool enabled)
         return;
     MP_VERBOSE(x11, "%s screensaver.\n", enabled ? "Enabling" : "Disabling");
     x11->screensaver_enabled = enabled;
+    if (xss_suspend(mDisplay, !enabled))
+        return;
     int nothing;
     if (DPMSQueryExtension(mDisplay, &nothing, &nothing)) {
         BOOL onoff = 0;

wscript

@@ -578,6 +578,7 @@ video_output_features = [
         'name': '--x11',
         'desc': 'X11',
         'func': check_pkg_config('x11',         '>= 1.0.0',
+                                 'xscrnsaver',  '>= 1.0.0',
                                  'xext',        '>= 1.0.0',
                                  'xinerama',    '>= 1.0.0',
                                  'xrandr',      '>= 1.2.0'),