progs/tests: compile with SCons and glew

Also get mingw cross-compilation of these tests working
diff --git a/progs/tests/texrect.c b/progs/tests/texrect.c
index 43edc49..10061ee 100644
--- a/progs/tests/texrect.c
+++ b/progs/tests/texrect.c
@@ -6,11 +6,11 @@
  */
 
 
-#define GL_GLEXT_PROTOTYPES
 #include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <GL/glew.h>
 #include <GL/glut.h>
 #include "readtex.h"
 
@@ -328,6 +328,7 @@
    glutInitWindowPosition( 0, 0 );
    glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE );
    glutCreateWindow(argv[0] );
+   glewInit();
 
    Init( argc, argv );