Substantial rewrite (again) of decl handling.

The decl.* code now no longer interacts with Symbols, but just returns
names, types, initializer expressions, etc., as needed.  This makes the
code a bit more understandable.

Fixes issues #171 and #130.

tests/ptr-cast-complex.ispc

@@ -0,0 +1,18 @@
+
+export uniform int width() { return programCount; }
+
+export void f_f(uniform float RET[], uniform float aFOO[]) {
+    uniform int x[2][10];    
+    for (uniform int i = 0; i < 2; ++i) {
+        for (uniform int j = 0; j < 10; ++j) {
+            x[i][j] = 10*i+j;
+        }
+    }
+
+    uniform int (* varying y)[10] = x;
+    RET[programIndex] = y[1][programIndex % 5];
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 10+ (programIndex % 5);
+}