Curly braces fix

@jwilkes As discussed in private mail: Enables the curly braces so that they can be used as key presses and in object and message boxes.

These are excluded in the Tk-based Pd variants as they may cause issues with the Tcl component there, but this isn't the case with nw.js-based Purr-Data any more, so it would be nice to have these available there. The only reason to not allow them that I can see is to maintain bug compatibility with vanilla Pd. But I don't think that this should be a major consideration any more as long as legacy patches can still be loaded, and AFAICT the present merge request doesn't affect that capability in any way. OTOH, curly braces braces are part of the lexical syntax of many contemporary programming languages and data formats, so if these are to be supported by Purr-Data then it's important that the user can actually enter these characters. In particular, this lets me enter Pure vector literals on the canvas when programming Pd objects using the Pd-Pure extension (which is available for Purr-Data and works great with it, cf. http://puredocs.bitbucket.org/pd-pure.html).

This merge request is based on current HEAD and assumes !28 (merged), so the corresponding commit 9c58f4d3 is also included here. You can either merge this right away, or apply !28 (merged) first. In the latter case, I should probably rebase this once you've applied !28 (merged) to keep the history clean or you could just cherry-pick the latest commit 58509b69 from here if you've already applied !28 (merged).