getRootAs..() function now has a second implementation that
accepts an existing object to allow object reuse, much like
all other methods that refer to objects.
Change-Id: Iffef567c903a130761ef7de98867e5465d29a04d
Also fixed Go unit tests not being up to date with recent schema
changes.
Change-Id: I42e619f9c5ea05f6f937c68a5c8a92462c46bce3
Tested: on Linux and Windows.