*.cc: Remove explicit reference to 'testsuite/' in testcases.

       * testsuite/27_io/*.cc: Remove explicit reference to 'testsuite/'
       in testcases.  Prepare for the DejaGnu based framework.
       * mkcheck.in: Adjust call to tests_flags.  Don't mmkdir testsuite
       directory -- it is now mkcheck working directory.
       * tests_flags.in: Remove reference to $(top_srcdir).  Use
       ${SRC_DIR} instead.
       * Makefile.am (check, check-install): Change mkcheck invocation
       logic.
       * Makefile.in: Regenerate.

From-SVN: r39255