[Libreoffice] font dropdown list minor changes for script-relevant preview

[Caolán McNamara]

fdo#33510 basically boils down to that previewing the English/ASCII name
of a font in that font itself isn't that useful for some fonts because
lots of CTL fonts either can't render anything in the ASCII range or are
typically used for drastically different scripts.

So, here are some pics here on the intended results:
http://blogs.linux.ie/caolan/2011/02/09/small-libreoffice-font-dropdown-list-improvements/

This needs a little bit of per-platform font backendery, so the impl
I've now pushed hopefully doesn't break, too badly anyway, the win and
mac builds.

C.