Fix setindex to work for more index types.

[andreasnoack]

These were falling back on the implementation in abstractarray.jl for Colon so for this small example

julia> A = DistributedArrays.drandn(200,200);

julia> B = A[51:150,51:150];

julia> C = Array(Float64,100,100);

julia> @time C[:] = B;
  0.004728 seconds (5.18 k allocations: 294.531 KB)

I can see ~2000x speedup.

[codecov-io]

Current coverage is 70.12%

Merging #71 into master will increase coverage by <.01%

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[coveralls]

Coverage increased (+0.02%) to 70.123% when pulling 997895d on anj/setindex into 0215b9d on master.

[andreasnoack]

I should add here that it would be great to know to what extend the methods here fall back to the AbstractArray methods. It's quite disastrous when it happens because, unfortunately, many of the methods for AbstractArray fetch elements one at a time. At the same time, it can be tricky to detect. One solution is to debug this by removing the subtype relation between DArrays and AbstractArray and see if any of the tests fail.