Quoting :doc note-6-5:

  Improved the error message when encountering an illegal comma while
  reading input (i.e., for a comma not within a suitable nesting of
  backquotes). Thanks to Jared Davis for bringing this issue to our
  attention and for a helpful discussion.


git-svn-id: http://acl2-devel.googlecode.com/svn/trunk@1290 5d84a466-a78b-0930-a311-59b22171a541