localhost/default port

When creating federated table that points to unspecified host or
localhost on unspecified port or port is 0, small memory leak occurs.

This happens because we make a copy of unix socket path, which is
never freed.

With this fix we do not make a copy of unix socket path, instead
share->socket points to MYSQL_UNIX_ADDR constant directly.

This fix is covered by a test case for BUG34788.

Affects 5.0 only.


mysql-test/t/federated.test:
  A test case for BUG#35509.
sql/ha_federated.cc:
  When creating federated table we call parse_url() to check if connect
  string is correct. parse_url() may make a copy of unix socket path if
  port is not specified or 0 and host is not specified or 'localhost'.
  This copy is never freed.
  
  As there is no need to make a copy of unix socket path, let
  share->socket point to MYSQL_UNIX_ADDR directly.