repl: allow leading period in multiline input

When writing multiline input, one can't chain function calls as if the
lines begin with a period, since those are treated as REPL commands.

Before:

    > ([0, 1, 2]
    ... .map(x => x + 1))
    Invalid REPL keyword

After:

    > ([0, 1, 2]
    ... .map(x => x + 1))
    [ 1, 2, 3 ]

PR-URL: https://github.com/nodejs/node/pull/3835


Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>