Fix ticket 93.

 * src/code/reader.lisp:
   * Try to round really small numbers
   * Add somewhat more informative message when the number is not
     representable.
 * src/i18n/local/cmucl.pot:
   * Update
 * tests/trac.lisp:
   * Add test for ticket 93
   * Add a few comments for test trac.87.