Last year I provided rework of the assertion failure message when comparing XML by introducing XPath index.
Now I found that the current implementation can generate invalid XPath. The index could should apply to the parent.

This PR replaces #1272 to target 5.X

Input

Compare

<root>
  <xml1 />
  <xml1><xml2 /><xml2 a=\"x\" /></xml1>
  <xml1>
    <xml2 />
    <xml2 a=\"x\" />
  </xml1>
</root>

with

<root>
  <xml1 />
  <xml1><xml2 /><xml2 a=\"x\" /></xml1>
  <xml1>
    <xml2 />
    <xml2 a=\"y\" /> <!-- note the different attribute -->
  </xml1>
</root>

Expected behavior

Expected attribute "a" at "/root/xml1[3]/xml2[2]" to have value "y", but found "x".

Actual behavior

Expected attribute "a" at "/root/xml1[3]/xml2[4]" to have value "y", but found "x".