src: PagedPage: instance will drop references on dispose stage.
src: PagedWindow: implemented dispose GObject virtual function.
src: TestPaged: added test case for weak reference @ PagedPage:page-holder
src: TestMockPageHolder: fix syntaxes to compile
src: TestPaged: on test_paged_page_property_weak_page_holder, make use of TestMockPageHolder instead of PagedWindow which is another subject of test.
src: TestMockPageHolder: emit page's removed signal before unrefing it.
src: PagedPage: added property page-holder, changed page_holder field into GWeakRef, to be more thread-safe.
src: PagedPage: added paged_page_get_page_holder (getter for page-holder)
src: TestPaged: eliminated most of warnings, and added test_paged_page_build_from_xml() to test custom child type in GtkBuilder feature
src: PagedWindow: added initialized for internal state, and makes sure when page is ref_sinked when it is added.
src: TestPaged: added test_paged_window_add_remove and little tidy up.