* Added rational util functions used by Fraction class not
  available in the boost::rational class.
* Replaced usage of Fraction by boost::rational<long>
* Removed code that relies on:
  1. fraction.IsValid() -- rational only allow valid values, ie
     denominator() != 0
  2. rational.denominator() == 0 -- always false
  3. rational.denominator() < 0 -- always false but implementation
     detail: http://www.boost.org/doc/libs/release/libs/rational/rational.html#Internal%20representation
* Simplified code that relies on:
  1. rational.denominator() != 0 -- always true
* BUGS EXIST because Fraction allows the creation of invalid values but
  boost::rational throws the exception boost::bad_rational

Change-Id: I84970a4956afb3f91ac0c8f726547466319420f9
Reviewed-on: https://gerrit.libreoffice.org/11551Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>