Avoid a gcc warning about shadowing a global variable.

* subversion/libsvn_subr/x509parse.c
  (latin1_to_utf8): Change index variable name to i.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/svn-auth-x509@1616638 13f79535-47bb-0310-9956-ffa450edef68