Ensure implementation and specification entries are present in MANIFEST.MF

[basil]

Fixes an (unreleased) regression introduced in #247.

[Vlatombe]

@basil This makes plugin packaging fail badly (cryptic Caused by: java.io.IOException: invalid header field) if the maven project>description contains a newline character. By the way, shouldn't Specification-Title be project.getName() instead?

[basil]

Sorry, I somehow clicked edit rather than reply. Here is my reply:

@basil This makes plugin packaging fail badly (cryptic Caused by: java.io.IOException: invalid header field) if the maven project>description contains a newline character.

Thanks for the notification. Was this an informational notification, or are you implying that I should take some sort of action as a result of this notification?

By the way, shouldn't Specification-Title be project.getName() instead?

You tell me. Should it? Shouldn't it? Why? Why not?