fixed total test count on junit port. throwing error for non-existing ports.

- an error is now thrown (XSP03) when you refer to a non-existing port using `x:document`
- the junit output port now counts the total amount of tests correctly. fixes #20
- removed the main test.xprocspec document. invoke all the individual files instead (done automatically when building using xproc-maven-plugin)
Merge branch 'issue-20'