Fix two problems:

Fix two problems:
- The value of mysqli_get_client_info() has been changed recently and did
not include "mysqlnd" anymore thus the test suite was thinking the build
is always libmysql. This did not kept the suite from running pconn tests
- Going back to the libc allocator because the memory arena could be on a
  persistent connections. If the build is not debug there will be no error
  but the memory will be freed and in the second use of this pconn freed
  memory will be used - not good! For now the arena doesn't take an argument
  whether it should allocate persistently or not, thus persistent is safe
  for now.

Johannes gave his +1 to commit this.