[LyX/master] Reduce the amount of needed boost headers

[Pavel Sanda]

On Sat, Dec 12, 2020 at 07:05:38PM +0200, Yuriy Skalko wrote:
> > By the way, when you are already digging into the internal workings of
> > preview loader, would it be hard to allow mutliple threads loading
> > graphics images in backgrounds instead of single one?
> > Documents with lot of figures take a long time to load fully and most
> > of nowadays machines have multiples cores, to do that job in parallel.
> > 
> > Pavel
> 
> Yes, this should be really useful. I'll check it.

BTW did get to it? Pavel