Add wxActivityIndicator control.

This is a simple animated control indicating some program activity.

Provide native GTK+ (for > 2.20) and OS X implementations as well as a generic
one used under MSW.

Update the sample and the documentation.

samples/widgets/makefile.gcc

@@ -29,6 +29,7 @@ WIDGETS_CXXFLAGS = $(__DEBUGINFO) $(__OPTIMIZEFLAG_2) $(__THREADSFLAG) \
 	-Wall -I. $(__DLLFLAG_p) -I.\..\..\samples -DNOPCH $(__RTTIFLAG_5) \
 	$(__EXCEPTIONSFLAG_6) -Wno-ctor-dtor-privacy $(CPPFLAGS) $(CXXFLAGS)
 WIDGETS_OBJECTS =  \
+	$(OBJS)\widgets_activityindicator.o \
 	$(OBJS)\widgets_bmpcombobox.o \
 	$(OBJS)\widgets_button.o \
 	$(OBJS)\widgets_checkbox.o \
@@ -252,6 +253,9 @@ clean:
 $(OBJS)\widgets.exe: $(WIDGETS_OBJECTS) $(OBJS)\widgets_sample_rc.o
 	$(CXX) -o $@ $(WIDGETS_OBJECTS)  $(__DEBUGINFO) $(__THREADSFLAG) -L$(LIBDIRNAME) -Wl,--subsystem,windows -mwindows $(____CAIRO_LIBDIR_FILENAMES_p) $(LDFLAGS)  $(__WXLIB_ADV_p)  $(__WXLIB_CORE_p)  $(__WXLIB_BASE_p)  $(__WXLIB_MONO_p) $(__LIB_SCINTILLA_IF_MONO_p) $(__LIB_TIFF_p) $(__LIB_JPEG_p) $(__LIB_PNG_p)   -lwxzlib$(WXDEBUGFLAG) -lwxregex$(WXUNICODEFLAG)$(WXDEBUGFLAG) -lwxexpat$(WXDEBUGFLAG) $(EXTRALIBS_FOR_BASE) $(__CAIRO_LIB_p) -lkernel32 -luser32 -lgdi32 -lcomdlg32 -lwinspool -lwinmm -lshell32 -lcomctl32 -lole32 -loleaut32 -luuid -lrpcrt4 -ladvapi32 -lwsock32 -lwininet
 
+$(OBJS)\widgets_activityindicator.o: ./activityindicator.cpp
+	$(CXX) -c -o $@ $(WIDGETS_CXXFLAGS) $(CPPDEPS) $<
+
 $(OBJS)\widgets_bmpcombobox.o: ./bmpcombobox.cpp
 	$(CXX) -c -o $@ $(WIDGETS_CXXFLAGS) $(CPPDEPS) $<