ports-mgmt/pkg-devel: Update to 1.16.99.1

Changes from 1.15.99.8 to 1.16.99.1

• Avoid making making xstring.h public
• audit: fix quiet
• libpkg: add a snap(shot) version prefix
• libpkg: only upgrade installed packages with pattern matches
• libpkg: accept an "rsa:" prefixed file for pkg_finish_repo()

Approved by: bapt (implicit)