RFR 8196074: Remove uses of loose type equality tests

[Maurizio Cimadamore]

Hi,
this patch is the result of the discussion we had in this thread:

http://mail.openjdk.java.net/pipermail/compiler-dev/2018-January/011593.html 


The goal is to remove the 'loose' type equality check from javac, in 
order to achieve better alignment with the spec.

Thanks to B. Blaser for contributing to this effort.

Patch here:

http://cr.openjdk.java.net/~mcimadamore/8196074/

Cheers
Maurizio