Feature: #7: VSync

- Add VSync feature. 3 possible VSync methods available: "sw" (software,
  not too reliable, but at least you have something to fallback to),
  "drm" (using DRM_IOCTL_WAIT_VBLANK, should work only on DRI drivers),
  "opengl" (using SGI_swap_control extension OpenGL, might work on more
  drivers than the DRM method). "sw" and "opengl" are briefly tested,
  "drm" received utterly no test (because I use the nVidia binary blob).
  They are enabled with "--vsync sw" / "--vsync drm" / "--vsync opengl".

- Add --refresh-rate to let user specify a refresh rate for software
  VSync, in case the automatic refresh rate detection does not work
  well.

- Seemingly the automatic refresh rate detection using X RandR in
  software VSync detects refresh rate incorrectly. Need further investigation.

- Fix a few bugs in fading timing.

- Add a workaround for client window detection on Fluxbox, as Fluxbox
  (incorrectly?) sets the override-redirect flag upon all frame
  windows.

- Software VSync adds dependency on librt (a part of glibc) for
  nanosecond-level timing functions, and libXrandr for automatic refresh
  rate detection; DRM VSync adds dependency on libdrm to use its drm.h,
  but does not link to libdrm; OpenGL VSync adds dependency on libGL.

- Print timing information on DEBUG_REPAINT.

README.md

@@ -45,6 +45,7 @@ __R__ for runtime
 * libxfixes (B,R)
 * libXext (B,R)
 * libxrender (B,R)
+* libXrandr (B,R)
 * pkg-config (B)
 * make (B)
 * xproto / x11proto (B)
@@ -52,6 +53,8 @@ __R__ for runtime
 * xprop,xwininfo / x11-utils (R)
 * libpcre (B,R) (Will probably be made optional soon)
 * libconfig (B,R) (Will probably be made optional soon)
+* libdrm (B) (Will probably be made optional soon)
+* libGL (B,R) (Will probably be made optional soon)
 
 To build, make sure you have the above dependencies: