It is no longer legal to initialize arrays and structs with single

scalar values (that ispc used to smear across the array/struct
elements).  Now, initializers in variable declarations must be
{ }-delimited lists, with one element per struct member or array
element, respectively.

There were a few problems with the previous implementation of the
functionality to initialize from scalars.  First, the expression
would be evaluated once per value initialized, so if it had side-effects,
the wrong thing would happen.  Next, for large multidimensional arrays,
the generated code would be a long series of move instructions, rather
than loops (and this in turn made LLVM take a long time.)

While both of these problems are fixable, it's a non-trivial
amount of re-plumbing for a questionable feature anyway.

Fixes issue #50.

tests/packed-store-3.ispc

@@ -3,7 +3,9 @@ export uniform int width() { return programCount; }
 
 export void f_f(uniform float RET[], uniform float aFOO[]) {
     float a = aFOO[programIndex]; 
-    uniform int pack[2+programCount] = 0;
+    uniform int pack[2+programCount];
+    for (uniform int i = 0; i < 2+programCount; ++i)
+        pack[i] = 0;
     uniform int count = 0;
     if ((int)a & 1)
         count += packed_store_active(pack, 2, a);