The XPATH implementation was not handling correctly the XPATH 
production #19 
(http://www.w3.org/TR/1999/REC-xpath-19991116/#node-sets),
namely

PathExpr ::= | FilterExpr '/' RelativeLocationPath
                    | FilterExpr '//' RelativeLocationPath

It was lacking context for the RelativeLocationPath and it was just 
ignoring the second slash instead of treating it as a different axis 
specifier.
Fixed the above two problems and added a test case.