Add support for int8/int16 types. Addresses issues #9 and #42.

failing_tests/shuffle2-10.ispc

@@ -0,0 +1,16 @@
+
+/* failing due to llvm bug http://llvm.org/bugs/show_bug.cgi?id=10421 */
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    int8 aa = aFOO[programIndex]; 
+    int8 bb = aa + programCount;
+    int8 shuf = shuffle(aa, bb, 2*programIndex+(int)b-5);
+//CO    print("%\n%\n%\n%\n", aa, bb, 2*programIndex+(int)b-5, shuf);
+    RET[programIndex] = shuf;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 1 + 2*programIndex;
+}