2.8.15:

* Correct initialization when using --disable-deprecated to reduce the API.
  Bug #426931
  (Johannes Schmid, Openismus)
* Do not discard signals documentation. (Armin Burgmeier, Openismus)
* OptionGroup: Preserve default values again, after this fix was lost.
  (Armin Burgmeier)
* Build:
  - Fix the build with m4 1.4.8, avoid mkstemp problems.
  (Dodji Seketeli, Daniel Elstner)