Fix a make dist bug

RTSP rewind and fastforward support (Scale option). Almost entirely rewritten a patch from K. Staring <Qdk _at_ quickdekay dot net>.

* This is untested, but shouldn't have any adverse effect at least
* Any feedback much welcomed

* updated the po-files, started some work on the German translation, a minor string fix and removal of an untranslatable string

* when possible use the PTS for GET_TIME and GET_LENGTH. Note that this isn't always reliable. If you want you can disable it.

* use intf_IntfProgress instead of intf_UserProgress to test the interaction-implementations. Additionally, it's nicer here IMO, so we might keep it this way.