Add test covering unpacking 0-length rdatas
Make TestDynamicUpdateZeroRdataUnpack pass

Straight up: took a guess and the tests pass.
Test that Msg.RemoveRRset() works as intended
Make RemoveRRset work as intended
Lose a loop in Msg.RemoveRRset() and use copyHeader()

Per @miekg's advice
Merge pull request #154 from andrewtj/atj-update-misc

DNS Update Misc
go test -short

Added a bunch a long running test function to the list of skipped
tests when giving -short to go test. Tests are bascially *all*
DNSSEC key generation tests and 1 serving test.

PASS
ok      github.com/miekg/dns    0.782s

Compared to 13+ s, so quite a bit faster.
Do test -short in travis as well