Check that Symbol properties are proper, and support downlevel type checking

tests/cases/conformance/Symbols/ES5SymbolProperty1.ts

@@ -0,0 +1,11 @@
+//@target: ES5
+interface SymbolConstructor {
+    foo: string;
+}
+var Symbol: SymbolConstructor;
+
+var obj = {
+    [Symbol.foo]: 0
+}
+
+obj[Symbol.foo];

tests/cases/conformance/Symbols/ES5SymbolProperty2.ts

@@ -0,0 +1,11 @@
+//@target: ES5
+module M {
+    var Symbol;
+
+    export class C {
+        [Symbol.iterator]() { }
+    }
+    (new C)[Symbol.iterator];
+}
+
+(new M.C)[Symbol.iterator];

tests/cases/conformance/Symbols/ES5SymbolProperty3.ts

@@ -0,0 +1,8 @@
+//@target: ES5
+var Symbol;
+
+class C {
+    [Symbol.iterator]() { }
+}
+
+(new C)[Symbol.iterator]

tests/cases/conformance/Symbols/ES5SymbolProperty4.ts

@@ -0,0 +1,8 @@
+//@target: ES5
+var Symbol: { iterator: string };
+
+class C {
+    [Symbol.iterator]() { }
+}
+
+(new C)[Symbol.iterator]

tests/cases/conformance/Symbols/ES5SymbolProperty5.ts

@@ -0,0 +1,8 @@
+//@target: ES5
+var Symbol: { iterator: symbol };
+
+class C {
+    [Symbol.iterator]() { }
+}
+
+(new C)[Symbol.iterator](0) // Should error

tests/cases/conformance/Symbols/ES5SymbolProperty6.ts

@@ -0,0 +1,6 @@
+//@target: ES5
+class C {
+    [Symbol.iterator]() { }
+}
+
+(new C)[Symbol.iterator]

tests/cases/conformance/Symbols/ES5SymbolProperty7.ts

@@ -0,0 +1,8 @@
+//@target: ES5
+var Symbol: { iterator: any };
+
+class C {
+    [Symbol.iterator]() { }
+}
+
+(new C)[Symbol.iterator]

tests/cases/conformance/Symbols/ES5SymbolType1.ts

@@ -0,0 +1,3 @@
+//@target: ES5
+var s: symbol;
+s.toString();

tests/cases/conformance/es6/Symbols/symbolProperty58.ts

@@ -0,0 +1,8 @@
+//@target: ES6
+interface SymbolConstructor {
+    foo: string;
+}
+
+var obj = {
+    [Symbol.foo]: 0
+}