Merge pull request #225 in SNORT/snort3 from ~MIALTIZE/snort3:for-russ to master

Merge pull request #225 in SNORT/snort3 from ~MIALTIZE/snort3:for-russ to master

Squashed commit of the following:

commit 65ec53744d1f200275a4aed1b021fecfe45edf90
Author: Michael Altizer <mialtize@cisco.com>
Date:   Tue Feb 2 17:12:23 2016 -0500

    extra: Use pkg-config to retrieve Snort includes dir, remove explicit option

commit af06110d9e32bab85b443c72ee290005cbc95899
Author: Michael Altizer <mialtize@cisco.com>
Date:   Tue Feb 2 17:11:00 2016 -0500

    snort.pc: Only export CPPFLAGS as Cflags (should be further pruned/controlled)

commit d6ecbb16ba40638a120c11c0d0baf11bb85ba257
Author: Michael Altizer <mialtize@cisco.com>
Date:   Tue Feb 2 11:21:12 2016 -0500

    extra: Prefer clang compiler like Snort does.

commit 8539fc0f7e4fee80ee4e90b07a0fbd14a1416b3d
Author: Michael Altizer <mialtize@cisco.com>
Date:   Tue Feb 2 11:19:23 2016 -0500

    snort.pc: Add Snort install dir to CPPFLAGS includes

    Note: This is sort of an ugly subversion of pkg-config, but I'm just
    following suit.

commit 6f1795ad3db90b468d3c6ae2d4e7e47c97806e64
Author: Michael Altizer <mialtize@cisco.com>
Date:   Mon Feb 1 16:00:47 2016 -0500

    sfdaq: Conditionally support new-style daq_modify_flow()

commit 3ca33d0ad7839e3583e2630a949c94284e15ce68
Author: Michael Altizer <mialtize@cisco.com>
Date:   Tue Jan 19 13:47:10 2016 -0500

    Remove DAQ_GetAddressSpaceID.  We don't support LibDAQ versions without address space ID anymore.

commit 88707f0f4cfb74ef108c7880a710b0345d8d040f
Author: Michael Altizer <mialtize@cisco.com>
Date:   Mon Jan 4 15:38:02 2016 -0500

    autoconf: Prefer clang over gcc for CC to match CXX