Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add some missing definitions to build a working FreeBSD's libusb under Linux.

- Make the FreeBSD's USB library compile under Linux.
- Fix a compile warning where the return value of a call
to a write() function was ignored.
- Remove redundant include files from userland USB header files.
- Add some now needed include files to various C-files.