Checks that err:XD0001 is raised if more than one document
      appears as connection on p:variable and @connection
      is missing. (This error is only raised if the context item is referenced.)
Test ab-variable-021.xml is expected to fail with error code err:XD0001.
<p:declare-step xmlns:err="http://www.w3.org/ns/xproc-error" xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
   <p:output port="result">
   <p:variable name="var" select="count(.)">
      <doc/>
      <doc/>
   </p:variable>
   <p:identity>
      <p:with-input>
         <doc>{$var}</doc>
      </p:with-input>
   </p:identity>
</p:declare-step>
Adapted test to new context item strategy, new error code.
Fixed test; the error is only raised if the context item is referenced.
Fix namespace declarations
New tests. Some tests changed to new order in p:pipe
Some tests fro p:variable