net/fping: Update to 3.13

• Use new official GitHub repo, as website was down from Apr-Sept 2016
• Add USES=autoreconf as GitHub tarball only comes with configure.ac
• Add USES=gmake as manpage generation was failing with pmake

Changes this release:

https://github.com/schweikert/fping/blob/3.13/ChangeLog

PR: 212386
Approved by: jharris@widomaker.com (maintainer), adamw (mentor)