* Bug 16665 fixed: help('echo') can redirect to help('mode') on preferences

* Bug 16665 fixed: help('echo') can redirect to help('mode') on preferences

  http://bugzilla.scilab.org/16665

  Interactive test:
  // Preference unchecked (default):
  help echo  // => list of possible matching pages displayed on the left
  preferences
      // General/Documentation : check "Redirect Matlab terms to closest Scilab equivalent"
      // validate and quit
  help echo  // => display the mode() page
  help cot   // => display the cotg() page. etc

Change-Id: I5129c130592fefb99180eb44d8abe245a00db7c0