Preventing cyclic dependencies among bundled plugins.

Reproducible for example via HelpLinkTest.testMatrixConfig.
Otherwise have: matrix-project → script-security → matrix-auth → windows-slaves → antisamy-markup-formatter → matrix-project
Tried to come up with a generic way of doing this automatically, but failed.
Just because we bundle a particular build of some plugin does not mean it was built against anything recent,
and for use on older cores it may well need some of those implicit dependencies.