title: Eclipse plugin project "checkstyle internal error" says "cannot initialize module TreeWalker - Unable to instantiate '...ForbidCertainImportsCheck'"
body: <p>I haven't looked at my Eclipse plugin project for a few weeks, but after I updated to Neon.1, I  noticed the following error in the Problems view:</p>
  
  <blockquote>
    <p>Checkstyle execution failed due to an internal error. Please check the error log for details.</p>
  </blockquote>
  
  <p>In the error log, I saw things like this:</p>
  
  <blockquote>
    <p>!MESSAGE Checkstyle-Plugin: cannot initialize module TreeWalker - Unable to instantiate
    'com.github.sevntu.checkstyle.checks.coding.ForbidCertainImportsCheck' class,
    it is also not possible to instantiate it as com.puppycrawl.tools.checkstyle.checks.annotation.com.github.sevntu.checkstyle.checks.coding.ForbidCertainImportsCheck,
    com.puppycrawl.tools.checkstyle.checks.blocks.com.github.sevntu.checkstyle.checks.coding.ForbidCertainImportsCheck,
    [deleted numerous similar class names],
    com.puppycrawl.tools.checkstyle.com.github.sevntu.checkstyle.checks.coding.ForbidCertainImportsCheckCheck.
    Please recheck that class name is specified as canonical name or read how to configure short
    name usage <a href="http://checkstyle.sourceforge.net/config.html#Packages" rel="nofollow">http://checkstyle.sourceforge.net/config.html#Packages</a>. Please also
    recheck that provided ClassLoader to Checker is configured correctly.</p>
  </blockquote>
  
  <p>After I saw this in my neon.1 workspace, I also noticed that my older workspace running in Mars.2 was also showing the same problem.</p>