Allows homebrew formulas to declare any taps they require, in a preamble.
Allow formulas the option of suppressing caveats of dependent formulae.  A composite formula may want to summarize all the caveats of its dependents.
Source an event to the containing formula, just after each dependent formula fully installs.  This can help when one dependent needs a prior dependent to be more than just installed, but also initialized.  For example, after "ruby-build", the parent formula could build ruby 1.9.3, after ruby-build installs fully, but before the next dependent of SideKiq gets started.