When trying to auto-complete after a ". " string, join the auto-completion with the "."

This lets the user do the following in a Processing buffer:

    FloatList foo;
    foo. |                <-- cursor is here
    foo. float|[list.add] <-- cursor needs to be separated from "foo." to start the auto-complete
    foo.add               <-- pressing RET joins the "add" with the "foo."