Update libsigc++ to 2.6.1:

2.6.1 (stable):

* Add back deprecated adaptors/lambda API to avoid an unintented ABI break.
  (Kjell Ahlstedt) Bug #755550 (Michael Biebl)
* sigc::trackable: Move operations: Don't move the callback list
  (Kjell Ahlstedt) Bug #755393 (Tom Schoonjans)

2.6.0 (stable):

* C++11: deduce_result_type: Simplify with C++11 variadic template.
  (Murray Cumming, Marcin Kolny) Bug #753612
* Fix the build with MSVC.
  (Chun-wei Fan) Bug #754082
* Update the website.
  (Kjell Ahlstedt)

2.5.4 (unstable):

* slot_base::operator=(const &): Copy the blocked too,
  so the destionation is blocked if the source is blocked,
  regardless of whether the destionation was previously
  blocked, because this seems to be what we should expect.
  (Murray Cumming)
* C++11: slot_base, slot*, signal_base, signal*, trackable:
  Add move operations.
  (Murray Cumming)
* Update MSVC Projects, requiring at least MSVC++ .Net 2013
  for C++11 support.
  (Chun-wei Fan)

2.5.3 (unstable):

* Use C++11 "using" aliases to simplify code that uses type traits.
  (Murray Cumming) Bug #753580

2.5.2 (unstable):

* Remove useless headers:
    sigc++/class_slot.h
    sigc++/hide.h
    sigc++/method_slot.h
    sigc++/object.h
    sigc++/object_slot.h
    sigc++/retype.h
  Some of these still have equivalents in sigc++/adaptors/
  (Kjell Ahlstedt, Murray Cumming) Bug #752560
* C++11: Replace deprecated std::auto_ptr by std::unique_ptr.
  (Kjell Ahlstedt)
* C++11: Use std::is_base_of<> instead of our sigc::is_base_and_derived<>,
  removing sigc::is_base_and_derived<>.
  (Kjell Ahlstedt, Murray Cumming) Bug #752560
* C++11: Use of range-based for loops.
  (Murray Cumming)
* C++11: Use of the auto keyword.
  (Murray Cumming)
* C++11: Use of nullptr instead of 0.
  (Murray Cumming)
* sigc++/slot.h: Use a regular .h file instead of generating it
  from an .m4 file. Bug #752560
  (Kjell Ahlstedt)
* Visual Studio Builds: Move 2010 Projects to 2012 to support C++11.
  (Chun-wei Fan)
* Use -Wformat-security and -Wshadow with --enable-warnings=fatal.
  (Murray Cumming)

2.5.1 (unstable):

* Use (and require) C++11
  (Kjell Ahlstedt)
* Using C++11 lambda functions to create sigc::slots:
  Avoid the need for SIGC_FUNCTORS_DEDUCE_RESULT_TYPE_WITH_DECLTYPE.
  (Kjell Ahlstedt)
* Remove the already-deprecated sigc::lambda (and sigc::group) API.
  This is an API change but should not be an ABI change, so it should
  only affect you when rebuilding applications, if you use this API.
  (Murray Cumming, Kjell Ahlstedt)


(wiz)