Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.Approved by: re (implicit)Sponsored by: The FreeBSD Foundation
Add dcons_os.{c,h}.
Add dumb console driver and related bits.dcons(4): very simple console and gdb port driverdcons_crom(4): FireWire attachmentdconschat(8): User interface to dconsTested with: i386, i386-PAE, and sparc64.