Xrandr support in the X11 target.

Fixes Bugzilla #109, and as a bonus, Bugzilla #145, too!

docs/html/sdlenvvars.html

@@ -576,6 +576,18 @@ algorithm. It can be in decimal or in hex (prefixed by 0x).</P
 ><DT
 ><TT
 CLASS="LITERAL"
+>SDL_VIDEO_X11_NO_XRANDR</TT
+></DT
+><DD
+><P
+>If set, don't attempt to use the Xrandr extension for resolution mode
+switching.  Normally Xrandr takes precedence over the XF86VidMode
+extension, so setting this environment variable will cause the 
+XF86VidMode extension to be used if it is available.</P
+></DD
+><DT
+><TT
+CLASS="LITERAL"
 >SDL_VIDEO_YUV_DIRECT</TT
 ></DT
 ><DD
@@ -1209,4 +1221,4 @@ VALIGN="top"
 ></DIV
 ></BODY
 ></HTML
->
+>