Is.unsorted nanoival method

Test if a `nanoival` vector is Not Sorted

Test if an object is not sorted (in increasing order), without the cost of sorting it.

## S4 method for signature 'nanoival'
is.unsorted(x, na.rm = FALSE, strictly = FALSE)


`x`	a `nanoival` vector
`na.rm`	logical. Should missing values be removed before checking?
`strictly`	logical indicating if the check should be for _strictly_ increasing values.