progs: Port most of the demos to glew.

A couple of test weren't ported due to glew breakage -- it undefines
GLAPIENTRY.
diff --git a/progs/demos/copypix.c b/progs/demos/copypix.c
index 15001e8..51435ac 100644
--- a/progs/demos/copypix.c
+++ b/progs/demos/copypix.c
@@ -6,11 +6,10 @@
  */
 
 
-#define GL_GLEXT_PROTOTYPES
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <GL/glew.h>
 #include <GL/glut.h>
 
 #include "readtex.h"
@@ -234,6 +233,7 @@
       glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE);
 
    glutCreateWindow(argv[0]);
+   glewInit();
 
    Init(ciMode, filename);
    Usage();