Library package naming is libsigx-<version>-<soversion> where <version> and
<soversion> are obtained from the name of the actual library file, in e.g.
/usr/lib/libsigx-2.0.so.2, as per documented
here: http://www.netfort.gr.jp/~dancer/column/libpkg-guide/libpkg-guide.html#id250154

Eventhough this isn't a libtool library, the versioning used is the same as
libtool's versioning. Also, considering sigx is an extension to sigc++, its
package naming convention has been mirrored closely, considering that upstream
is mirroring sigc++'s version.

A debian/*.symbols file is not used, because C++ name mangling seems to breaks 
this on different platforms/architectures.
