Added tests and documentation for soa<> rate qualifier.

tests/soa-22.ispc

@@ -0,0 +1,35 @@
+
+struct Point { float x, y, z; };
+
+struct Foo {
+    int x;
+    Point *pts[3];
+    int8 z;
+};
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    float a = aFOO[programIndex]; 
+
+    soa<8> Foo * uniform pts = uniform new soa<8> Foo[4];
+//CO    uniform Foo pts[32];
+    foreach (i = 0 ... 32) {
+        pts[i].x = b*i;
+        pts[i].z = -b*i;
+        for (uniform int j = 0; j < 3; ++j) {
+            pts[i].pts[j] = new uniform Point[4];
+            for (uniform int k = 0; k < 4; ++k) {
+                pts[i].pts[j][k].x = 100*i+10*j+k;
+                pts[i].pts[j][k].y = -1234;
+                pts[i].pts[j][k].z = -(100*i+10*j+k);
+            }
+        }
+    }
+    
+    RET[programIndex] = pts[programIndex].pts[programIndex % 3][programIndex % 4].z;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = -(100*programIndex+10*(programIndex % 3)+(programIndex % 4));
+}