libsigc++ implements a typesafe callback system for standard C++. It
allows you to define signals and to connect those signals to any
callback function, either global or a member function, regardless
of whether it is static or virtual.

This is the 1.2 version of libsigc++, which is outdated, but required
by some packages that haven't been updated to use 2.0 yet. This package
doesn't conflict with the main libsigc++ package.
