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

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

Import x86emu from OpenBSD as of OPENBSD_4_6.

Import x86emu from OpenBSD (src/sys/dev/x86emu).

x86emu is a software emulator for the real mode x86 processor, originally
written by SciTech Software, Inc. for XFree86 and has been later ported
to NetBSD then OpenBSD.