Libreoffice update 4.2.5

LibreOffice 4.2.5.2. Non-breaking dependency addition pushed to master previously.

Builds and starts on x86_64-linux.

One failing test disabled (the problem is not a regression w.r.t. our build of 4.0, though). Maybe massive update-everything would fix it, but such an update is better done in x-updates. This update seems to be master-ready.

Source download generator rewritten, some dependency shuffling (sometimes splitting the build outside of the main expression), small build fixes.

Will merge in a couple of days unless there are any objections/improvements. Maybe anyone wants to keep multiple versions?