OS X improvements

I have finally had some time to play with geany on OS X and found a few problems these patches try to address. For my installation I used the quartz backend as described here: http://wiki.geany.org/howtos/osx/running

The biggest issue is that paste doesn't work - the issue is in Scintilla (well, rather in gtk-quartz but it's easier to workaround in Scintilla). I've already submitted the patch here: https://sourceforge.net/p/scintilla/bugs/1677/

The second biggest problem is the infinite loop in find in files which should be fixed now.

The rest are minor problem fixes and fixes of warnings comping from clang.

One more patch to mention is the ui_get_mime_icon() improvements - it fixes the case (which is a bit surprising) when GIcon is returned but the icon actually doesn't exist (haven't seen this happen on Linux, but it happens on OS X and I believe on Windows too). It also replaces the "stock ID" (which for some reason doesn't work) with "icon name" which works (e.g. for folder icons). I haven't found since which GTK version icon names are supported so I hope it works on older GTK too.

After the patches, Geany is quite usable (and nice-looking) on OS X - the only issue I'm aware of is the non-functional VTE terminal (terminal tab shows but it's empty all the time). But I suspect VTE here - I compiled libvte and tried the supplied demo vte application and it doesn't work either.