[CF-Devel] destroying barrels

[Mark Wedel]

 I only did a quick look at the code, and haven't tested this.  But it appears
that all barrels need to be destroyable is some hp value that is non zero.

 boulders would also need some material type I believe, but physical attacks
would still otherwise be able to destroy them.

 someone should probably verify this will work, and then perhaps update the maps
that really need this feature to work.