Fix problems related to the saving and retrieval of drafts

This is a series of patches intended to fix problems related to the saving and retrieval of drafts that include a quoted message.

See the individual commit messages for specifics.

Related issues:  [4782](https://code.google.com/p/k9mail/issues/detail?id=4782), [5010](https://code.google.com/p/k9mail/issues/detail?id=5010), [5634](https://code.google.com/p/k9mail/issues/detail?id=5634), [5725](https://code.google.com/p/k9mail/issues/detail?id=5725)