Fix RANDR’s gamma_to_ramp().

In order to generate a 256-entry ramp in [0,65535] which covers the full
range, one must mupliply eight-bit values not by 256 but rather by 257.

Many years back – well before the RANDR extension was written, and
before xorg@fdo – a similar bug fix was made to the DIX for converting
client-supplied eight-bit color values into sixteen-bit values.

Noticed by: Elle Stone and Graeme Gill.

Signed-off-by: James Cloos <cloos@jhcloos.com>

hw/xfree86/modes/xf86RandR12.c

@@ -1679,11 +1679,11 @@ gamma_to_ramp(float gamma, CARD16 *ramp, int size)
 
     for (i = 0; i < size; i++) {
         if (gamma == 1.0)
-            ramp[i] = i << 8;
+            ramp[i] = i | i << 8;
         else
             ramp[i] =
                 (CARD16) (pow((double) i / (double) (size - 1), 1. / gamma)
-                          * (double) (size - 1) * 256);
+                          * (double) (size - 1) * 257);
     }
 }