keyring: check keyring usability and disable remember password function accordingly.
Merge pull request #89 from Aetf/keyring-check-patch

Check keyring usability and disable remember password function accordingly
Add comment about gnome-keyring; https://github.com/LiuLang/bcloud/issues/63#issuecomment-62442552
Merge branch 'master' of github.com:LiuLang/bcloud