Fallback `reconstruct` method provides incorrect error message

[bertini97]

Given a valid pca::PCA, calling reconstruct(pca, y) with y that is not an AbstractVecOrMat will call the fallback method, which errors saying

'reconstruct' is not defined for PCA{T}

when it's not true. This should be handled differently.

MultivariateStats.jl/src/types.jl

Line 27 in b7dc36e

reconstruct(model::AbstractDimensionalityReduction, y) = error("'reconstruct' is not defined for $(typeof(model)).")

[anurag-mds]

This looks like a misleading fallback rather than a missing method. reconstruct(::PCA, ""AbstractVecOrMat) is defined but the failure occurs when y has the wrong type.
a clearer error message like we can explicitly mention the expected type or we can remove this generic fallback and provide a MethodError which makes it more accurate.
If this sounds good and resaonable then I can take a PR...