ACTION-2050 - Change all xsd: to xs:

All,

This is done, in both documents.

I notice that the XPath Expressions Module [1] uses `xf:` as prefix for
XForms, for example:

    xf:relevant() as xs:boolean

There are a few places where `xforms:` is used. `xforms:` is used more
generally in the main spec [2], but some of the newer examples use `xf:`
too.

So we should harmonize that too. I like the idea of using `xf:` all over
for the XForms namespace, and `xh:` for XHTML. What do you think?

-Erik

[1] https://www.w3.org/community/xformsusers/wiki/XPath_Expressions_Module
[2] https://www.w3.org/community/xformsusers/wiki/XForms_2.0