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)