Log Message:
Update to 2.4.0:

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)

2.3.2 (unstable):

Note: The implementation of bug #724496 breaks API for some users,
but it does not break ABI.
Only users who have added their own visit_each() overloads are affected by
the API break. Their programs will still compile, but there will be run-time
errors, if they rely on auto-disconnection of slots.
Updated instructions for users who implement their own adaptors are found
in the description of sigc::adapts<>.

* Replace visit_each() overloads by struct visitor<>.
  Add the test_visit_each test case.
  (Ryan Beasley, Kjell Ahlstedt) Bug #724496
* signal_impl::notify(): Don't delete signal_impl during erase().
  (Kjell Ahlstedt) Bug #564005 (Alexander Shaduri)
* Fix 'make check' with clang++ 3.4 and --enable-warnings=fatal
  (Kjell Ahlstedt) Bug #724496 (Ryan Beasley)
* Fix test_cpp11_lambda for gcc 4.8
  (Kjell Ahlstedt)
* Speed up disconnection of slots.
  (Kjell Ahlstedt) Bug #167714 (Neal E. Coombes)
* Auto-generate the ChangeLog from the git log for 'make dist'.
  (José Alburquerque)
* Don't use __file__ in the FIREWALL m4 macro.
  (Kjell Ahlstedt) Bug #699168 (John Ralls)
* Add the track_obj() adaptor and test_track_obj test case.
  Deprecate libsigc++ lambdas, sigc::group() and sigc::var().
  Use C++11 lambda expressions instead.
  (Kjell Ahlstedt) Bug #672555
* Documentation:
  - Emphasize that signals are reference counted.
    (Kjell Ahlstedt) Bug #611941 (Jonathon Jongsma)
  - Mention std::function<> and std::bind() where appropriate.
    (Kjell Ahlstedt, Chris Vine)
  - Use DOXYGEN_SHOULD_SKIP_THIS consistently to exclude internal
    functions from the reference documentation.
    (Kjell Ahlstedt)
* Windows:
  - Enable C++11 lambda expressions with MS Visual Studio 2012 and later
    (Ryan Beasley) Bug #733752
  - Update MSVC_Net2010
    (Kjell Ahlstedt) Bug #724496 (Ryan Beasley)

2.3.1 (unstable):

* signal_base: Add blocked(), block(), unblock().
  (Kjell Ahlstedt) Bug #153780