tests setup: less hard-coding of the test subdirectory * t/ax/tests-init.sh: Make the code creating the temporary test subdirectory smart enough to automatically create it in the same subdirectory of the test that is being run. * defs-static.in ($MKDIR_P, $am_rel_srcdir): New variables, AC_SUBST'd from @MKDIR_P@ and @srcdir@ respectively, and used in the new 'tests-init.sh' code. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>