- SC_NO_SYSMOUSE isn't currently supported by vt(4), so nuke it from vt.4.
- vt_vga(4) is a driver rather than a function so reference it accordingly.
- Uncomment HISTORY section given that vt(4) will first appear in 9.3.

Reviewed by:	emaste (modulo last part)
MFC after:	3 days
Sponsored by:	Bally Wulff Games & Entertainment GmbH
Minor mdoc fix.
Correct the buffer length check to avoid overflows.

Found with:	Coverity Scan
CID:		1222502, 1222503