Fix unnecessary inclusion of glibmm/threads.h. This can be resolved by ensuring that glibmm headers always preceed glib.h headers. Same applies with gtkmm/gtk+ etc
Change marker layout in stroke-widget so they are all on one line.
Adding inclusion of config.h where needed for threads.h check.
Added configure/ifdef guards to only bring in the needed #include if glibmm has it.
Correct to compile against recent gtkmm, including updated macports versions. Fixes bug #1179338.
Fix for 165865 : Fix marker color on duplicate
Fix for 165865 : markers must take object's stroke color
Fix for 1030239 : Custom markers only added to the list in 'Fill and Stroke - Style' after reloading the file : Fix selection regression
Fix for 1030239 : Custom markers only added to the list in Stroke Style after reloading the file
Fix for 943225 : Replace Gtk::OptionMenu with Gtk::ComboBox