Updating v3 parent POM to HttpClient 4.3

[Brent Putman]

Since I'm doing a lot of work on HTTP-related components, I thought this
might be a good time to update to the latest HttpClient version 4.3
(we're currently on 4.2).  Looks like some interesting things there[1],
including new builder classes and some changes in the way they do authN,
which might help with some issues I noticed while working on the
HTTPMetadataResolver. 

Does anyone know of a reason *not* to upgrade us to 4.3?

Thanks,
Brent


[1]
http://www.apache.org/dist/httpcomponents/httpclient/RELEASE_NOTES-4.3.x.txt