sysutils/s6-rc: Upgrade to version 0.6.0.0

Changes from NEWS file:

• Bugfixes.
• Support for shared libraries on MacOS.
• New: s6-rc-repo-* and s6-rc-set-* binaries, the "repo"

collection of tools to help with management of source definition
directories.

• The boot database is now configurable at build time (--bootdb)

and the default is now /etc/s6-rc/compiled/current.

• Some commands now accept long options.
• s6-rc-compile is less verbose on -v2.