vsHeap now takes a name, used when tracing leaks
Adjust line width based on screen resolution.

This means that we should get approximately the same glow effect
regardless of the resolution, since bright lines will use the same
percentage of the screen, regardless of resolution.  (Previously, they
were rendering as single-pixel-wide lines, which resulted in lines being
thinner at higher resolutions, which resulted in there being fewer
and dimmer glowing pixels in the low-resolution glow buffer)