[[[
Extend the SVN_ERR macro with another parameter, a cleanup statement, that is
executed before returning in case of error.

* subversion/include/svn_error.h
  (SVN_ERR_EX): New macro. Similar to SVN_ERR, it accepts an additional
    parameter for a cleanup statement to execute before returning an error.
  (SVN_ERR): Expand to SVN_ERR_EX with the same expression, and a no-op for the
    cleanup statement.
]]]