Add an optional context to the test driver's assertions.

 * test/abts: Add context to all assertion functions, add new assertion
              helper macros with a context parameter.
 * test/testxml.c: Adjust the direct call to abts_str_equal.
 * test/testxlate.c: Add the conversion context to the expected result check.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1935444 13f79535-47bb-0310-9956-ffa450edef68