Add option to lock keyring

[vinipsmaker]

I've made a commit that add an option to lock the keyring.

How to use:

# Lock the default keyring
$ gkeyring.py --lock
# Lock the 'login' keyring
$ gkeyring.py --lock --keyring login

[kparal]

I'll have a look at the patch as soon as I find a little spare time. Thanks for your work.

[vinipsmaker]

I'll have a look at the patch as soon as I find a little spare time.

Thanks. I'll be waiting.
=)

[kparal]

Thanks, pushed.