XQuery needs to prohibit variable redefinition

[Michael Kay]

> 
> Can I join the choir?  :-)  I've seen customers hit that same variable
> confusion. 
> 

And we just had another newbie fall right into the hole on the xsl-list a
few minutes ago. Though with a variation: they were using a global and a
local variable of the same name, which XSLT has always allowed. 

Mike