o added GladeSignalEditor::detail-suggestions signal
  o Fixed memory leak on handler-suggestion emmision

gladeui/glade-signal-model.c: Removed "__dummy" object data hack
  Now only the data model returns user strings like <Type Here> when the GladeSignal value is null

gladeui/glade-signal.c: fixed bug in glade_signal_set_detail() that allowed to set an empty string as a detail