Add failing completion test

[fhammerschmidt]

Added the failing test mentioned in #643

The funny thing is, I tried to change the Js.log("Hello") to a () which made the second completion work as well. No idea what's going on there.

[cristianoc]

Looks like it's not what comes before, but what follows.

First

Completable: Cpath Value[ReactEvent, ""]

then

Completable: Cpath Value[ReactEvent, "", log]

so parser recovery somehow picks up log too.

[cristianoc]

For context, this is a correct program:

module S = {
type r = {xx:int}
}

let r = {S.xx:10}

let f = r.
S.xx

so playing with parser recovery is a little tricky in these cases.

[cristianoc]

@fhammerschmidt should behave as expected now.
There's some logic to detect when foo. (with empty space) is followed by a valid possible path continuation, but it would not handle well the situation where the path after . has more than 1 element.