`wrbrushes` includes illusionary detail brushes as solids

[DaZombieKiller]

While running some stress tests using ad_sepulcher.map as a sample, I noticed that compiling with wrbrushes will result in vines suddenly becoming solid geometry. It appears that func_detail_illusionary brushes (and possibly others) are given a solid contents value:

These should probably either be (optionally?) omitted from the BRUSHLIST lump, or given a non-solid contents value.