The ewarn message says: "To allow parallel installation of sig++-1.0, sig++-1.2, and sig++2.0 the header files are now installed in a version specific subdirectory. Be sure to unmerge any libsig++ versions < 1.0.4 that you may have previously installed." however it should probably say libsigc++ instead of libsig++, and sigc++ instead of the occurrences of sig++ (note the extra 'c'). thanks.
Easy fix... Thanks for pointing this out.