Finished up "overload collapsing" for navigate-to.

Current semantics:
  - If an overload lacks an implementation, go to the first implementation.
  - If an overload has any implementation, go to the first one.
  - If there are any declarations between an implementation and any overload, this will split the series of overloads (note that this is invalid code).

tests/cases/fourslash/navigationItemsOverloadsBroken1.ts

@@ -24,6 +24,6 @@
 ////    throw overload;
 ////}
 
-verify.navigationItemsListCount(1, "overload1", "exact");
+verify.navigationItemsListCount(2, "overload1", "exact");
 verify.navigationItemsListCount(2, "overload2", "exact");
-verify.navigationItemsListCount(3, "overload", "prefix");
+verify.navigationItemsListCount(4, "overload", "prefix");

tests/cases/fourslash/navigationItemsOverloadsBroken2.ts

@@ -0,0 +1,23 @@
+/// <reference path="fourslash.ts"/>
+
+////function overload1(a: string): boolean;
+////function overload1(b: boolean): boolean;
+////function overload1(x: any, b = (function overload() { return false })): boolean {
+////    throw overload1;
+////}
+////function overload1(b: number): boolean;
+////function overload1(f: typeof overload): boolean;
+
+////function overload2(a: string): boolean;
+////function overload2(b: boolean): boolean;
+////function overload2(x: any, b = (function overload() { return false })): boolean {
+////    function overload2(): boolean;
+////    function overload2(x: any): boolean;
+////    throw overload2;
+////}
+////function overload2(b: number): boolean;
+////function overload2(f: typeof overload): boolean;
+
+verify.navigationItemsListCount(1, "overload1", "exact");
+verify.navigationItemsListCount(3, "overload2", "exact");
+verify.navigationItemsListCount(4, "overload", "prefix");