Added tests for 'void' return type compatibilty on overloads and implementations.

tests/cases/conformance/functions/functionOverloadCompatibilityWithVoid01.ts

@@ -0,0 +1,4 @@
+function f(x: string): number;
+function f(x: string): void {
+    return;
+} 

tests/cases/conformance/functions/functionOverloadCompatibilityWithVoid02.ts

@@ -0,0 +1,4 @@
+function f(x: string): void;
+function f(x: string): number {
+    return 0;
+} 

tests/cases/conformance/functions/functionOverloadCompatibilityWithVoid03.ts

@@ -0,0 +1,4 @@
+function f(x: string): void;
+function f(x: string): void {
+    return;
+}