ctest: fix add_subdirectory() crash

The directory is at args[0], not args[1].  Introduced in commit
v2.6.0~489 (... 5889 ... tests are not found in some cases when using
add_subdirectory ..., 2008-01-18).

Source/CTest/cmCTestTestHandler.cxx

@@ -176,7 +176,7 @@ bool cmCTestAddSubdirectoryCommand
   cmSystemTools::ChangeDirectory(cwd);
   std::string fname = cwd;
   fname += "/";
-  fname += args[1];
+  fname += args[0];
 
   if ( !cmSystemTools::FileExists(fname.c_str()) )
     {