title: Check if aspectjweaver (or any javaagent) is loaded
body: <p>Is there a (pref portable) way to check if 
  The JVM has been stated with a particular  <code>-javaagent</code>?</p>
  
  <p>In particular I'm interested to know if the aspectj load time weaver has loaded or not. (I'm trying to provide a helpful error msg in the case of incorrect startup).</p>