scons: Build progs together with everything else.

This is a substantial reorganization, This particular commit enables:
- building the progs for unices platforms
- glew is now built as a shared library (it is the default, and it is
inconvenient and pointless to shift away from that default)
- all progs get built by default

progs/samples/SConscript

@@ -1,23 +1,5 @@
 Import('*')
 
-if not env['GLUT']:
-    Return()
-
-env = env.Clone()
-
-env.Prepend(CPPPATH = [
-	'../util',
-])
-
-env.Prepend(LIBS = [
-	util,
-	'$GLUT_LIB'
-])
-
-if env['platform'] == 'windows':
-    env.Append(CPPDEFINES = ['NOMINMAX'])
-    env.Prepend(LIBS = ['winmm'])
-
 progs = [
     'accum',
     'bitmap1',
@@ -52,7 +34,7 @@ progs = [
 ]
 
 for prog in progs:
-    env.Program(
+    progs_env.Program(
         target = prog,
         source = prog + '.c',
     )