Fix test that fails to compile in Java 8 due to new boxing changes.

Given a method with the following signature

      <T> T getT()

and two overloads

      void m(int, int)
      void m(Object, Object)

a call like

     m(1, getT())

is ambiguous.

Change-Id: I8aa51c1a8106e32e23e114997427786d969f7609
Adds recursive file change listen support.

Accumulated file changes will later be useful to shortcut
ResourceOracle rescans.

Change-Id: I10ee002c5752084a715e9c116aff8d46aaf33945
Review-Link: https://gwt-review.googlesource.com/#/c/10130/