FormulaInstaller: move post_install handling into finish
FormulaInstaller: inline effective_deps instead of memoizing
FormulaInstaller: break up really long line
FormulaInstaller: don't check pour_bottle? in build_time

pour_bottle? will still be true when pouring a bottle failed, but we
still want to print the build time if we've fallen back to building from
source. The check for @start_time.nil? will prevent the build time from
being printed when pouring bottles.
FormulaInstaller: re-expand deps when pouring a bottle fails