2.99.9: (unstable)

* signal_impl::clear(): Don't clear the slot list during signal emission,
  to prevent a segfault. And add a test for this.
  (Kjell Ahlstedt) Bug #784550 (Andrejs Hanins)
* Remove signal_base::erase() and signal_impl::erase().
  (Kjell Ahlstedt) Bug #784550
* Various minor code cleanups.
  (Murray Cumming)
* Windows: Update the MS Visual Studio build.
  (Chu-wei Fan)