Improved pango text integer attributes editors.
Make the spin button numeric and clear the attr if the new text is an empty string!

This should be enough to close Bug 679006
"The "size" attribute for labels only accepts integer values (not strings like "larger")"
Fixed Bug 679079 "Glade changes the "homogenous" packing property of toolbar buttons to "yes""
Fixed glade_gtk_image_get_property() chainup. (was calling set_property)
Fixes bug that prevented the runtime object to show the right pixbuf when copying a GtkImage.
Added workaround for Bug 625867 "RadioButton information lost on cut+paste, add/remove parent, etc"
Added extra check in glade_project_verify_signal_internal()
because it the widget could not have an associated project.
Fixed bug when copying a button with custom content.
Custom widget was being replaced with a placeholder when syncing
custom-child property.