Merge: Ropefix

A few modifications to ropes, I discovered that the `+` routine used to create too many Concat nodes passed a certain point, which inceased the RAM use of Strings unnecessarily (might help with #1106's example program, on my machine the memory went from 200M+ used to 20M).

While I was at it, I removed a few old-style-inits that were no longer necessary.

Some others however I could not remove, maybe there is a way I can do so, but with the spec of the new constructors I'm not entirely sure how to do so without retaining unnneeded information or complexifying instanciation, that'll have to wait.

Pull-Request: #1127
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>