dns: fix protocol yaml setting

UDP code would accidentally depend on 'tcp' setting.
http: per tx decoder events

Store HTTP decoder events per TX, so they can be inspected per TX.

Ticket: #839.
app-layer: fix AppLayerParserProtocolIsTxEventAware

AppLayerParserProtocolIsTxEventAware would check if a proto is tx
event aware by checking if it had registered a StateHasEvents function.
However, this is an optimization function. This patch changes it to
use the StateGetEvents function instead, which is a better indicator.