bpo-37177: make IDLE's search dialogs transient (GH-13869)

This avoids the search dialogs being hidden behind the editor window.
diff --git a/Lib/idlelib/searchbase.py b/Lib/idlelib/searchbase.py
index 4ed94f1..6fba0b8 100644
--- a/Lib/idlelib/searchbase.py
+++ b/Lib/idlelib/searchbase.py
@@ -54,6 +54,7 @@
         else:
             self.top.deiconify()
             self.top.tkraise()
+        self.top.transient(text.winfo_toplevel())
         if searchphrase:
             self.ent.delete(0,"end")
             self.ent.insert("end",searchphrase)
@@ -66,6 +67,7 @@
         "Put dialog away for later use."
         if self.top:
             self.top.grab_release()
+            self.top.transient('')
             self.top.withdraw()
 
     def create_widgets(self):