Added context everywhere (by adding it to the binding attributes)

I added the context attribute to the binding attributes: 
http://www.w3.org/MarkUp/Forms/wiki/XForms_2.0#Binding_Attributes

This is a Category:XForms20 feature: 
http://www.w3.org/MarkUp/Forms/wiki/@context_everywhere

Cheers,
John M. Boyer, Ph.D.
Distinguished Engineer, IBM Forms and Smarter Web Applications
IBM Canada Software Lab, Victoria
E-Mail: boyerj@ca.ibm.com 

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