Clean up comments and whitespace characters in source files

Remove all remaining "last changed" version info from source comments.
(The version control system maintains this information automatically.)

Delete the trailing whitespace characters.

contrib/tools/makesRGB.c

@@ -1,6 +1,4 @@
 /* makesRGB.c -- build sRGB-to-linear and linear-to-sRGB conversion tables
- *
- * Last changed in libpng 1.6.0 [February 14, 2013]
  *
  * COPYRIGHT: Written by John Cunningham Bowler, 2013.
  * To the extent possible under law, the author has waived all copyright and
@@ -14,6 +12,7 @@
  * approximation to the 8-bit sRGB encoded value.  Calculate the error in these
  * tables and display it.
  */
+
 #define _C99_SOURCE 1
 #include <stdio.h>
 #include <math.h>