Remove some signatures for chksquare and make the ... version type stable

[andreasnoack]

As pointed out by @KristofferC in #12452, there is a type stability problem with chksquare(Factorizations). E.g.

julia> Base.return_types(LinAlg.chksquare, (LinAlg.LU,))
1-element Array{Any,1}:
 Union{Array{Int64,1},Int64}

This is fixed by these changes.

[vtjnash]

AppVeyor got confused (assigned two jobs the same number). AFAICT the build can not be restarted from here, so you'll have to force-push a new SHA1 hash if you want to trigger a new build.

(also Travis is having issues with their Mac cluster, so those are backed up right now too)