better fix for mga#12280 while fixing exit reported by Colin

previous fixes for mga#12280 resulted in Colin reporting mgaapplet
exiting (not segfaulting):

"When updates a bubble pops up:
- If you click on the background of this bubble, mgaaplet exits
- If you click on the "Install Updates" button, it pops up the password
  dialog.  Without touching anything, about 1s later the dialog seems to
  be replaced with another that says "Sorry, that didn't work, please
  try again". When this dialog appears, mgaapplet exits."

So let's clean the pile of fixes and:
- have only _one_ gtk+ main loop
- creating _one_ hidden notification before entering the main loop
- never destroy it, but use >close + >clear_actions() then ->update()
  prior calling >show() when one need to show a notification again

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 027a5c5c..aa541063 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,5 @@
+- better fix for mga#12280 while fixing mgaapplet exiting reported by
+  Colin
 - workaround gnome-shell not exiting message tray mode when clicking on actions
   (bgo#706783)