Add checks for uninitialized integers?

Something I found while fixing thinags in 13837 is that we don't currently have anyway to set integer arrays (and I presume scaler ints) to an invalid value to check for uninitialized values. For floats we can set things to a nan. Maybe we should expand the set_nan code to set int arrays to -huge(int) as an invalid value? We won't get the nice crash on use we get with a nan but at least it will be easier to see when we haven't set an array properly.

Start by locating the existing set_nan implementation and reviewing how it handles float arrays. Use the context from issue 13837 to understand the uninitialized-array problem. Done means the intended integer initialization behavior is implemented and its effect can be verified for integer arrays and scalar integers.

Written by the indexing model from the issue text.