New feature "Do not store my password"

I have written a feature to be able to configure an account so that the ingoing and outcoming password won't be stored in the settings. It works like this:
 - I have added a checkbox "Don't store my password" in the account options.
 - At start such accounts are disabled (I put a text "[-]" in front of the account name in the account list to identify such accounts easily)
 - When you open the account, K-9 will ask you for the password(s) but won't store it in the properties, so that in remains in memory only until K-9 is closed. You can also press cancel to access the stored messages without entering a password.
 - There is also a new menu item in the menu on the account list to forget all sessions passwords without having to exit K-9.

Please tell me if you have any comment on my modifications.

PS: To disable an account as long as the password hasn't be entered, I have reused the existing "disabled" feature. This option was for imported accounts, for which K-9 doesn't know the password yet. The first time you open this account, K-9 ask you for the password and store it. I simply added the notion of session passwords, which won't be stored.

PS2: This modification would cover http://code.google.com/p/k9mail/issues/detail?id=1243