`getindex(::UnitRange, ::BlockedUnitRange)` isn't blocked

[mtfishman]

For example:

julia> using BlockArrays

julia> (1:4)[blockedrange([2, 2])]
1:4

while:

julia> Vector(1:4)[blockedrange([2, 2])]
2-blocked 4-element PseudoBlockVector{Int64}:
 1
 2
 ─
 3
 4

See this related comment: #347 (comment).

[jishnub]

Yes, this is a shortcoming in Base, so we'll need to work around this.