RelaxNGValidator bogus error messages, also probably bad schema error handling.

[nani]

RelaxNGValidator gives nonsense error messages for cases where it should tell you exactly what is wrong and what is not.

ERROR: RelaxNGValidator: Validation error: gaia/fauna_chicken:1: Expecting an element Resources, got nothing

In this case it fails to tell you, you have added an invalid element as an entry and instead makes you believe something completely unrelated is happening, like for example not having defined something you did in fact define (Resources element).

How to reproduce:

1) Go to the file simulation/templates/template_unit.xml

2) Add <PopulationBonus>0</PopulationBonus> inside <Cost> element after sibiling element <Population>

3) Run Caspian Sea (2v2) skirmish map

...
<Entity>
  <AIProxy/>
  <Cost>
    <Population>1</Population>
    <PopulationBonus>0</PopulationBonus>
    <BuildTime>1</BuildTime>
    <Resources>
      <food>0</food>
...

4) Many nonsense errors where none tell you <PopulationBonus> is invalid child element of <Cost>

[Vladislav Belov]

The problem is that we use a third party library libxml and particularly its RelaxNG.