Replicates all needed state between expanded functions

commit 5e6f06cf59
Author: Aaron Gutierrez <gutierrez.aaron.m@gmail.com>
Date:   Thu May 11 15:42:11 2017 -0400

    Fixed issue with aliasing local variables

    ISPC++ now produces valid code, or an appropriate error message, for all
    of my test cases.

commit bfe723e1b7
Author: Aaron Gutierrez <gutierrez.aaron.m@gmail.com>
Date:   Thu May 11 03:09:38 2017 -0400

    Actually copy the AST.

    Type replacement works except for function parameters.

commit f65b3e6300
Author: Aaron Gutierrez <gutierrez.aaron.m@gmail.com>
Date:   Thu May 11 01:19:50 2017 -0400

    [WIP] Remove cases for ForeachStmt and SymbolExpr

commit 2e28640860
Merge: 6a91c5d d020107
Author: Aaron Gutierrez <gutierrez.aaron.m@gmail.com>
Date:   Wed May 10 23:13:40 2017 -0400

    Merge branch 'master' into copy_ast

commit 6a91c5d5ac
Author: Aaron Gutierrez <gutierrez.aaron.m@gmail.com>
Date:   Wed May 10 11:11:39 2017 -0400

    Attempt to replicate AST when expanding polytypes

tests_ispcpp/varying.ispc

@@ -0,0 +1,14 @@
+floating foo(const uniform int a, floating b) {
+    floating out = b;
+    for (int i = 1; i<a; i++) {
+        out *= b;
+    }
+
+    return out;
+}
+
+export void square(uniform int N, uniform floating b[], uniform double out[]) {
+    foreach (i = 0 ... N) {
+        out[i] = foo(2, b[i]);
+    }
+}