RFR: 8199865: Avoid initializing ShortCache in ProxyGenerator

[Claes Redestad]

Hi,

by using Map<Object, Integer> instead of Map<Object, Short> (preserving 
shortness of values) we can avoid having ProxyGenerator depend on 
Short$ShortCache, which is a small startup and footprint win (since 
Integer$IntegerCache is 100% likely to have already been initialized):

http://cr.openjdk.java.net/~redestad/8199865/open.00/

Thanks!

/Claes