[Libreoffice] support for mono 2.8

[Andreas Radke]

After talking to our mono package maintainer there's probably a broken
pkgconfig call in LibO. We had a similar issue when building
kdebindings-csharp:

https://bugs.archlinux.org/task/21319

There's probably somewhere in the LibO build code a call like 

pkg-config --libs --cflags mono
that needs to be changed to 
pkg-config --libs --cflags mono-2

depending on the detected mono version. So far I couldn't find where the
mono flags are set.

See also
http://www.mono-project.com/Embedding_Mono#Updates_for_Mono_version_2.8.2B


-Andy