http: don't decode + to space by default

Libhtp decodes the + character in the query string to a space by default.
Suricata rules (e.g. etpro sid 2806767) are expecting to see the space in
the http_uri buffer.

Added an option per htp config to reenable this default behavior:

    query-plusspace-decode: yes

Bug #1035.
Give Suricata priority to receive packets over Linux with mPIPE.

When installing the rules to tell mPIPE to send packet to Suricata,
give it a higher priority than the default used by Linux. This way if
Linux also tells mPIPE to send it packets, Suricata will get them
instead, as long as Suricata is running.