2.4.0 (stable):

Note: API/ABI is the same as in release 2.3.2. Compared to stable
releases 2.2.x, the API has been broken regarding visit_each() functions.
See the NEWS entry for libsigc++ 2.3.2.

* Fix the test_lambda test case for MS Visual C++ 2013 and other
  C++11-compliant compilers.
  (Kjell Ahlstedt) Bug #734368 (Ryan Beasley)
* Add a missing #include in limit_reference.h.
  (Kjell Ahlstedt)
* Documentation:
  - Use doxygen-extra.css from the mm-common package.
    Requires mm-common 0.9.7 when configured to use maintainer-mode.
    (Kjell Ahlstedt)