pkgsrc freeze rules

• No changes to mk/ or pkgtools/pkg_install and other bootstrap packages without PMC approval
• Non-leaf package changes that affect more than 50 packages require PMC approval too. If you are not sure how many are affected, run finddepends(1) from pkgtools/revbump or ask.
• Other non-leaf package changes require pre-commit review by another pkgsrc developers; look for reviewers on IRC or on packages@. Mention this with "ok wiz@" or similar in the commit message.
• For leaf packages use your own judgement. In case of doubt, you can always ask on packages@.