This updates libsigc++ to version 2.2.10. Also there is now an
option to test the build. It creates native static and shared
libraries, and it compiles without error using clang, llvm, and gcc
from XCode-4.0.2 on OSX 10.6.8, x86_64. This library is a typesafe
callback framework for C++.
ClosesHomebrew/homebrew#8107.
Signed-off-by: Charlie Sharpsteen <source@sharpsteen.net>