#760 Allow importing of encrypted public keys

[kluk]

Currently, a public key attachment that is encrypted using PGP/Inline, is not detected (encrypted attachments have mimetype application/octet-stream), and thus will not be imported when you use the import button in enigmail.

This patch changes:
- detection of public keys: .asc.pgp is now detected as a public key;
- public keys are decrypted (if necessary) before trying to import them;
- fixes a bug where encrypted attachments with an accompying .sig detached signature are detected as just signed attachments instead of signed and encrypted attachments;
- correctly removes the tempfile after importing a key.

[Patrick Brunschwig]

Thanks for the patch.

There are two issues in onShowAttachmentContextMenu() on line 992:
1. currentAttachments[i] doesn't exist, I think that should be selectedAttachments[0]
2. the property .displayName may be undefined as you can see a little further down in the same method. This would lead to an exception. I have attached a sample mail that exhibits the error.

[kluk]

Thanks for the feedback, fixed :-)!

[Patrick Brunschwig]

Thanks, this looks a lot better :-)

Committed on master and 2.0-branch.