Fix bugs with handling of 'continue' statements in foreach_* loops.

tests/foreach-unique-8.ispc

@@ -0,0 +1,16 @@
+
+export uniform int width() { return programCount; }
+
+export void f_f(uniform float RET[], uniform float aFOO[]) {
+    uniform int k = 0;
+    int index = aFOO[programIndex/2];
+    foreach_unique(j in index) {
+        if (j & 1) continue;
+        ++k;
+    }
+    RET[programIndex] = k;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = programCount / 4;
+}