Fix non-contiguous reshapes in numba backend

[aseyboldt]

np.reshape(x, some_shape) fails in numba if x is not contiguous. This can lead to compilation failures. We can work around this by converting to a contiguous array if it is not already the case. This is happening in code in dim_shuffle where the output shape is (), so a valid input array will always be contiguous, but numba doesn't seem to realize this.

Fixes pymc-devs/nutpie#40.

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