An attempt to get PooledDataArray(falses(3)) working
An attempt to get PooledDataArray(falses(3)) working

I always end up with the error
```julia
julia> PooledDataArray(falses(3))
ERROR: in PooledDataArray: a not defined
 in PooledDataArray at /home/bates/.julia/DataFrames/src/pooleddataarray.jl:110
julia> which(PooledDataArray,falses(3))
PooledDataArray{N}(d::BitArray{N}) at /home/bates/.julia/DataFrames/src/pooleddataarray.jl:110
```
and I believe that the next call should be
```julia
julia> PooledDataArray(bitunpack(falses(3)), falses(size(falses(3))), Uint8)
3-element Bool PooledDataArray:
 false
 false
 false
```
which gives the desired result.

scls19fr/DataFrames.jl,pwoolcoc/DataFrames.jl,zhmz90/DataFrames.jl,maximerischard/DataFrames.jl,JuliaPackageMirrors/DataFrames.jl,ccphillippi/DataFrames.jl,maximerischard/DataFrames.jl,tkelman/DataFrames.jl,JuliaStats/DataFrames.jl,campanja-forks/DataFrames.jl,anriseth/DataFrames.jl,niloynibhochaudhury/DataFrames.jl,emilbayes/DataFrames.jl,armgong/DataFrames.jl,tshort/DataFrames.jl