fn:count with path argument that includes current node - to become runtime SDE

The fn:count, fn:exists, fn:exactly-one, fn:empty functions take a path expression.

The precise meaning of these is not (yet) defined by the DFDL spec if the argument is a path that leads to an enclosing element where the expression resides.

Ex: fn:count(../..) when parsing? It is unclear what this means, and it is problematic if this relative path is to an enclosing array that contains elements where this expression is being evaluated at parse time, because success of the expression determines the count. This is inherently circular, or overly-constrains implementations to an iterative sequential parse algorithm.

The DFDL Workgroup has discussed clarification of this behavior, and the very likely result is that use of an argument path (relative or absolute) that refers to an enclosing element will be defined to be a runtime SDE.

Step 1 however, is to scan existing test suite and known DFDL schemas used with Daffodil, and to find any such usage. It is expected any such usage can be revised so as not to depend on this undefined DFDL behavior. 

All 4 functions: fn:count, fn:exists, fn:exactly-one, and fn:empty must be considered.

Then, detection and issuing of this runtime SDE should be implemented, and negative tests that cause this error added to Daffodil.