title: How can an SBT plugin depend on another plugin
body: <p>I want to write a plugin "MyPlugin" that depends on the another plugin 
  ("io.spray" %% "sbt-twirl" % "0.6.0").</p>
  
  <p>Simply adding sbt-twirl in libraryDependencies will not work,
  because plugins get published with a different path scheme
  than standard libraries.</p>
  
  <p>I also cannot declare sbt-twirl as a plugin dependency to MyPlugin
  project, because MyPlugin does not use the sbt-twirl directly,
  it is the project using MyPlugin that will indirectly use it.</p>
  
  <p>MyPlugin provides a task that is meant to be run after sbt-twirl
  has generated it's sources (in sourceManaged) and after compilation.</p>
  
  <p>A simple but non ideal solution would be to require the project using
  MyPlugin to also declare sbt-twirl as a plugin dependency, but it is not
  DRY because the two plugins will be sharing some settings (directories, versions, etc), 
  and they will have to be repeated and compatible.</p>