Fixed long line support in make-manifest.

Leiningen generates MANIFEST.MF files and then has the Manifest class read, parse, and re-write them. However, Leiningen generates invalid manifest files: it does not break lines the way it should. (The spec says no lines longer than 72 characters.)

This change fixes manifest generation to split long lines. It also adds a regression test which fails in unpatched leiningen.