Update run_tests and examples makefile for scalar target.

Fixed a number of tests that didn't handle the programCount == 1
case correctly.

tests/extract-1.ispc

@@ -3,9 +3,9 @@ export uniform int width() { return programCount; }
 
 export void f_f(uniform float RET[], uniform float aFOO[]) {
     double a = programIndex;
-    RET[programIndex] = extract(a, 3); 
+    RET[programIndex] = extract(a, min(programCount-1, 3)); 
 }
 
 export void result(uniform float RET[]) {
-    RET[programIndex] = 3;
+    RET[programIndex] = (programCount == 1) ? 0 : 3;
 }