* Windows Build:
- Define GLIBMM_DLL when building with mingw32 or cygwin,
because it is needed by gtkmm. Bug #309030
(Cedric Gustin)
* OptionGroup: Allow default values, by not initializing them all.
(Armin Burgmeier)
* Slight code size reduction by marking private functions as static.
(Murray Cumming)
