Fix a problem with the USB keyboard driver not properly handling key rollover resulting in duplicate keypress events.
Fix a problem with the USB keyboard driver not properly handling key
rollover resulting in duplicate keypress events.

PR:		57273
PR:		63171
Submitted by:	plasma <plasma at freebsd.sinica.edu.tw>
Submitted by:	Brian Candler <B.Candler at pobox.com>
MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase