RFR: 8163449: Allow per protocol setting for URLConnection defaultUseCaches

[Michael McMahon]

Could I get the following API (and impl) change reviewed please?

The change is to add a getter and setter in j.n.URLConnection
for a per-protocol default setting for the useCaches flag. With this
change it will be possible to switch off caching for the jar: protocol
but leave it switched on for http: etc.

http://cr.openjdk.java.net/~michaelm/8163449/webrev.1/

Assuming there is agreement I will file the CCC request.

Thanks
Michael.