Possible fix for #149 - #188

I think the reason the rpath was not touched if set already in linuxdeployqt is that too many assumptions were made while this was implemented. The only reason linuxdeploy does this this way is because linuxdeployqt does, too. I do not think it makes sense to just ignore the rpath altogether.

We should instead try to add (prepend/append) $ORIGIN to an existing rpath if it doesn't contain the value already. Could you please update your PR to implement such a behavior? I'm not sure prepending makes a lot of sense, I'd rather append, I guess.

Main reason of this PR is to fix gstreamer plugin that is broken now. It's happened, because linuxdeploy override rpath that gstreamer-plugin set. And, maybe, it's a fix for #149.

We should instead try to add (prepend/append) $ORIGIN to an existing rpath if it doesn't contain the value already. Could you please update your PR to implement such a behavior? I'm not sure prepending makes a lot of sense, I'd rather append, I guess.

Done.

Thanks!