Remove debian/ directory. The lifecycle of the Debian packaging files is better maintained in the Debian pool's diff file. Removing these files makes the life of the GiNaC releaser easier.
[build] Set correct rpath for linking with CLN... ... so users won't get 'error while loading shared libraries: no such file or directory'. Also embed rpath into pkg-config meta data, so g++ `pkg-config --cflags --libs ginac` foo.cc actually works without any additional effort from the user side.