hoon: make +slab respect variance (%read) and return false
::
++ slab :: test if contains
|= {cog/@tas typ/type}
- =(& -:(~(find ut typ) %free [cog ~]))
+ ?= [%| *]
+ (~(find ut typ) %read ~[cog])
::
++ slap
|= {vax/vase gen/hoon} ^- vase :: untyped vase .*
