Recent files on OSX: Unicode filenames get munged after saving to and reading back from persistent config data (OSX defaults)

The superficial symptom is that items from the Recent files list seem to disappear when relaunching Purr Data on OSX, which doesn't happen on Linux.

Digging into this, I found that Unicode characters like Ü become U\u0308 (with the literal ASCII character sequence "\u0308", not the code point \u0308!) in the recentX defaults value on OSX. Obviously the Unicode glyph Ü a.k.a. U\u0308 gets "translated" to the literal 7-character sequence "U\u0308" when storing the defaults value. It seems that the defaults saving code is to blame here (which works by running the defaults program via system() on OSX), since sending the filename from the GUI to the engine seems to work ok (otherwise none of the open and save operations would work with such filenames on OSX).