Workable fix for #550: Range expressions behaving badly.

This makes behaviour of range expressions less embarrassing.. ;) 
When typing `for i in 1 .. 10 do` you would get `for i in 1 .CompareTo. 10 do`. 
This code just keeps track of the last character entered. If it was a dot and you type another dot, do not invoke auto-completion. This fixes the behaviour for all scenarios: list, seq, array, for expr.