Brimming with antiglare goodness

This gives headgear with significant brims (boonie, ballcap/postal
worker, cowboy, 10-gal) the SUN_GLASSES flag.

Since all of them wither block helmets or at least require fitting to
work with armored headgear, I think it's a fair enough upgrade.
Adds descriptions to item screen

This alerts folks to anti-glare gear; threw OVERSIZE in as well.
Merge pull request #7989 from KA101/booniefix

Brimming with antiglare goodness