Implement concussive damage on high-explosive rounds

[cmbasnett]

Large high-explosive rounds do not damage players who are in minimal cover even when very close to the blast radius. This leads to situations where a player can be prone behind a very small mount of dirt, and a Priest shell will land extremely close to the player, but the explosion origin is not in direct line-of-sight to the player, so absolutely no damage is done. The video below shows the problem very clearly. At 5:36 in the video, a 105mm round lands 1 meter away from the player, but he is completely unharmed.

https://youtu.be/rppLQn2Mr0Q?t=5m30s

To fix this, we should be able to specify a "concussive" damage value and radius, which ignores (or at least is not completely nullified by) line-of-sight. This will make long-range artillery barrages from vehicles like the Priest significantly more effective and terrifying.

[AndrewTheel]

This is a significant change and I think we should start with 1 thing at a time. So either the Priest shells specifically or perhaps mortar shells.

[handsm]

Mortar shells are quite light really. And the mortars in game are light mortars, more transportable.

Priest shells are 105mm HE. Same or equivalent are the Sherman 105 and the StuH. I'm sure artillery strikes are intended to simulate indirect fire from 105mm or equivalent guns. The Cromwell CS is a 95mm howitzer and a near equivalent, with similar intended role. The jagtiger's 128mm and the IS2's 122mm are higher velocity, primarily anti-tank weapons, but the shells are so big I'd think they'd have a similar concussive effect.