Allow compile using --with-rst2man.
Allow compile using --with-rst2man.

Copied from Varnish-Cache code

KristianLyng/vagent2,KristianLyng/vagent2,KristianLyng/vagent2,KristianLyng/vagent2,KristianLyng/vagent2,KristianLyng/vagent2,KristianLyng/vagent2