Comment 0 for bug 195698

Summary: when a "Master Password" dialog is shown, any operation that wants to
prompt for "Master Password" should attach to the existing dialog, not display a
new one.

This is a spin-off of bug 95397 (see bug 95397 comment #23).

Steps to repsoduce (copied from bug 95397 comment #6):
1) Make sure you have "Encrypt sensitive information" enabled.
2) Set up an NNTP account for a server that requires authentication (I am not
sure if passwd-protected POP or IMAP will act the same; if you do not have
access to passwd-protected NNTP server, you can try to emulate one by using
user_pref("mail.server.servernn.always_authenticate", true); ).
3) Make sure that auth information for that server is stored in the wallet.
4) Set biff ("check for new messages every 1 minutes") on that account.
5) Restart Mozilla (logging out of Password Manager will probably work the same,
but haven't tried it).
6) Go for lunch.

Expected: when you come back, you have at most one "master password" dialogs
waiting for you.

Actual: you'll have a *lot* of them.

It seems that every time Mozilla tries to check for new messages, the server
will ask for authentication and Mozilla will prompt for the "master password".

Alternative stepts to reproduce:
1) Make sure you have "Encrypt sensitive information" enabled.
2) Make sure you have save login information for at least two different login
forms (for example, Bugzilla's one and some other).
3) Tools -> Password Manager -> Logout
4) In two different browser windows, go to the two login forms from step (2).

Expected: Single "Master Password" dialog
Actual: Each window has it own.

While the first scenario could be considered networking's fault (it should have
realized that it needed the same password in all the cases) and could be covered
by the bug 95397, the second scenario seems to be a password manager issue.