[xml] XPath // vs. descendant-or-self

[François Delyon <f delyon satimage fr>]

With libxml 2.6.27, xpath expressions "//" and "descendant-or-self"  
behaves differently.

For instance, on an html document "//body" returns nothing, but  
"descendant-or-self::body" returns the body element.
If I change xmlXPathCanRewriteDosExpression into return 0, both  
expressions now return the body element (as in 2.6.24).

I can't understand if the bug is in xmlXPathRewriteDOSExpression or  
elesewhere.

Regards.
F.Delyon.