fixed MMatrix boundschecks, faster getindex

[chethega]

As remarked on JuliaLang/julia#29000, accessing an MArray, MMatrix, MVector sometimes pulls a stack copy. This patch avoids the stack copy, by using the pointer for getindex as well, not just for setindex.

[KristofferC]

Should the thrown bounds errors be BoundsError(v, i) etc?

[andyferris]

Cool! Thanks :)

Are the matrix and vector versions strictly necessary anymore? Perhaps we can delete those methods.

[chethega]

Yes (also for setindex!) and yes, removed the duplicates.

The boundschecks for cartesian index access are still broken, though.

[fredrikekre]

Any reason not to write this as @boundscheck checkbounds(v, i)?

[chethega]

Ok, this is fast. How do I fix the following?

julia> using StaticArrays
julia> M=MMatrix{2,2}(rand(2,2));
julia> M[3,1]
0.7134474216097795

[andyferris]

OK what's there looks great now :)

For Cartesian indexing it's the ..._scalar functions at the start of indexing.jl

[chethega]

Ok, I think this can be merged (from my perspective). Can we run a benchmark to see whether the pointer access or the boundscheck confuse the optimizer? As far as I can see all cartesian accesses were effectively @inbounds up to now, so that may slow down some relying code :(

[andyferris]

Let's roll with this.