debian: Make symlinks in RPATH point to libraries by SONAME
This means they don't stop working when the real path to a library happens to have changed, for example upgrading GLib 2.32.3 to 2.32.4, which changes the real file implementing the library from libglib-2.0.so.0.3200.3 to libglib-2.0.so.0.3200.4.
This is a blocker for upgrading GLib (or several other libraries in scout, really, but GLib is the only one for which we're actually likely to do that).
Edited by Simon McVittie