Fix #3804: Provide list of referenced vars to REPL
Fix #3804: Provide list of referenced vars to REPL

Supersedes #3805. Here is a comparison of master, #3805 and this commit:

    # master
    $ bin/coffee
    coffee> 1 %% 2
    TypeError: Array.prototype.indexOf called on null or undefined

    # #3805
    $ bin/coffee
    coffee> 1 %% 2
    1
    coffee> (_results = null; i) for i in [1, 2, 3]
    TypeError: Cannot call method 'push' of null

    # this commit
    $ bin/coffee
    coffee> 1 %% 2
    1
    coffee> (_results = null; i) for i in [1, 2, 3]
    [ 1, 2, 3 ]

sterpe/coffee-fmt