Problem: "greater than" and "less than" XPath operators appeared to have been implemented in reverse.
Fix: swap arguments to eq_func() and eq_func_reverse() to provide correct operation result.


mysql-test/r/xml.result:
  Adding test case
mysql-test/t/xml.test:
  Adding test case
sql/item_xmlfunc.cc:
  Pass argumemtns to eq_func() and eq_func_reverse() in correct order:
  nodeset argument first, then scalar argument.
  Also, fixing eq_func_reverse() to do correct conversion, e.g:
  "scalar > nodeset" into "nodeset < scalar" instead of wrong "nodeset <= scalar"
  "scalar >= nodeset" into "nodeset <= scalar" instead of wrong "nodeset < scalar".