In the C test framework, improve assertion failure messages.
In the C test framework, improve assertion failure messages.

* subversion/tests/svn_test.h
  (SVN_TEST_ASSERT): Mention that the condition being reported (e.g.
    "foo is valid") is an assertion that failed, because otherwise the error
    message looks like it's saying the condition ("foo is valid") is itself the
    error. Report the file and line number.
  (SVN_TEST_STRING_ASSERT): Report the file and line number.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion