Infer return type for permutedims

This is the same kind of issue as #4387, but in this case we should
be able to statically infer the return type of the array (at least as
long as we don't care to make permutedims([1, 2], [2, 1]) work, but
this currently throws anyhow).

Unfortunately this revealed a bug in type inference, which emits
statically infers typeof(dimsB) for BitArrays and SubArrays as

(Type{TypeVar(:_,Vararg{Int})},)

which leads to the wrong similar method getting selected and inlined. I
changed inference.jl to infer this as (Int...) which works, but Vararg
types give me the creeps and I'm not sure this is a complete solution.