- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

- Move scratch data from the USB bus structure to the USB device structure
so that simultaneous access cannot happen. Protect scratch area using
the enumeration lock. Also reduce stack usage in usbd_transfer_setup()
by moving some big stack members to the scratch area. This saves around
200 bytes of stack.
- Fix a whitespace.

MFC after: 1 week

Correctly list the usbloader dependencies.

Add defines to more easily allow a single threaded version of the FreeBSD
USB stack. This is useful for non-kernel purposes, like the loader.

Fix depend target.

Initial version of libusbboot, a fully stand-alone, single threaded and
functional compilation of the FreeBSD USB stack for use with boot loaders
and such.

Discussed with: Hiroki Sato, hrs @ EuroBSDCon