size of the buffer is not necessarily known, and which can replace the
"memset(str, 0, strlen(str))" idiom. Use it to clear buffers which may
have contained authentication tokens.
git-svn-id: svn+ssh://svn.openpam.org/svn/openpam/trunk@803 185d5e19-27fe-0310-9dcf-9bff6b9f3609