Made two mods to std/io/read-string-tests.lisp:
- Modified a test (and added a similar one) to reflect a bug fix in
  acl2-devel svn revision 1154, for a bug reported by Jared;
- Commented out a test that was running forever without hons.

Updated :doc note-6-4 for the above bug fix.


git-svn-id: http://acl2-books.googlecode.com/svn/trunk@2232 303c5b2c-9740-0410-b014-fd8f9db7be32