extensions: document that `testedwith = 'internal'` is special
Extension authors (notably at companies using hg) have been
cargo-culting the `testedwith = 'internal'` bit from hg's own
extensions, which then defeats our "file bugs over here" logic in
dispatch. Let's be more aggressive about trying to give extension
authors a hint about what testedwith should say.
to build a new macosx binary package:
install macpython from http://www.python.org/download/mac
install py2app from http://pythonmac.org/packages/
make sure /usr/local/bin is in your path
run bdist_mpkg in top-level hg directory
find packaged stuff in dist directory