RFR: 8153142: Cannot resolve multiple values from one response header

[Michael McMahon]

Could I get the following change reviewed please?

In some circumstances multi-valued response headers
were being ignored (except for the first occurrence).
The change fixes that problem. It also changes the
output of multi-valued request headers to be consistent with that.

So instead of sending two headers as:

X-Foo: val1, val2

they are sent as

X-Foo: val1
X-Foo: val2

It is still possible to do it the other way by constructing the
value string as a single header.

http://cr.openjdk.java.net/~michaelm/8153142/webrev.1/

Thanks,
Michael