Allow out of bounds indices in Not

[bkamins]

Originally posted at JuliaData/DataFrames.jl#2197.

The question is should we allow the following code:

julia> x = [1,2,3]
3-element Array{Int64,1}:
 1
 2
 3

julia> x[Not(4)]
ERROR: BoundsError: attempt to access 3-element Array{Int64,1} at index [Not(4)]

to work (and in this case just return [1,2,3]) instead of throwing an error?

[mbauman]

Personally, I'm in favor of the status quo, but I agree the DataFrame column name feels different than an out-of-bounds index.

[bkamins]

OK - we can change it only for column names. Thank you!