ports-mgmt/pkg-devel: update to 1.20.99.8

Changes:

• fix a race in vulnxml fetch trigger
• add a new data.pkg which contains a fully valid json and aim at replacing packagesite.pkg because extensible, continue to produce packagesite.pkg
• repo: remove ability to provide v1 repository format
• deduplicate code directly using libucl exporters instead of home backed ones
• undocument ftp support
• provide FreeBSD native sandboxing function in the library directly (packagekit)
• curl: provide libfetch compatiblity about HTTP_USER_AGENT
• New keywork: @override_prefix (pkgbase)
• repo: using threads instead of forks
• add: only generates .pkgsave when really needed