vga: adjust 800x600 timing.
vga: adjust 800x600 timing.

My value for video_lead was too conservative, and was starting video
early.  This caused unreliable sync on my monitor.  Now it precisely
matches VESA standards (or at least the hearsay version I have access
to).

Interestingly, everyone rounds the actual framerate, which turns out
to be 60.316 Hz.  Lost some time to chasing that "bug."

cbiffle/m4vgalib,cbiffle/m4vgalib,cbiffle/m4vgalib,cbiffle/m4vgalib