Ported the temporary cursor jitter fix from 2.7.3.

readme.html

@@ -314,6 +314,7 @@ version of GLFW.</p>
   <li>[X11] Added support for the <code>GLX_EXT_swap_control</code> extension as an alternative to <code>GLX_SGI_swap_control</code></li>
   <li>[X11] Added the POSIX <code>CLOCK_MONOTONIC</code> time source as the preferred method</li>
   <li>[X11] Bugfix: Calling <code>glXCreateContextAttribsARB</code> with an unavailable OpenGL version caused the application to terminate with a <code>BadMatch</code> Xlib error</li>
+  <li>[X11] Bugfix: A synchronization point necessary for jitter-free locked cursor mode was incorrectly removed</li>
   <li>[Win32] Removed explicit support for versions of Windows older than Windows XP</li>
   <li>[Win32] Bugfix: Window activation and iconification did not work as expected</li>
   <li>[Win32] Bugfix: Software rasterizer pixel formats were not discarded by the WGL_ARB_pixel_format code path</li>

src/x11_window.c

@@ -1736,6 +1736,11 @@ void _glfwPlatformPollEvents(void)
                                            window->width / 2,
                                            window->height / 2);
             window->X11.cursorCentered = GL_TRUE;
+
+            // NOTE: This is a temporary fix.  It works as long as you use
+            //       offsets accumulated over the course of a frame, instead of
+            //       performing the necessary actions per callback call.
+            XFlush( _glfwLibrary.X11.display );
         }
     }
 }