Squashed commit of the following:

commit 3fcf84a9a2673e1e1466ce5b114d7b73c257e515
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Fri Jul 28 12:00:31 2017 -0600

    Spirit: Brings in the last of the PktCommon interfaces.

commit d26ebd901ba4ba84910e99b4e728b98c30fa4c0b
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Fri Jul 28 09:54:52 2017 -0600

    Spirit: Add a few more PktCommon interfaces.

commit b5cb8041d50233a4abb8fb4d1dcef5428ae2c2b2
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Fri Jul 28 09:33:31 2017 -0600

    libc/termios:  Remember block comments before empty file sections.

commit 0fcab2c1c8c74442d40bd5e8c6af50a34f8a5821
Author: Sebastien Lorquet <sebastien@lorquet.fr>
Date:   Fri Jul 28 09:31:00 2017 -0600

    tcdrain implementation based on a new term ioctl

commit 797d4adf7d41068c671f0217d369b797b269de1a
Author: Stefan Kolb <Stefan.Kolb@avat.de>
Date:   Fri Jul 28 09:19:04 2017 -0600

    We discovered a problem with the samv7 mcan driver which results, under some circumstances, in a ...