fix panic for ParseDN with invalid input

fix BER length encoding bug for lengths over 128, with test

fix SearchResultEntry encoding bug, add test

fix tlsStarting deadlock on concurrent operations

add filter string output

explicit TLS handshake

set isTLS for TLS connections from the start

make StartTLS work

add Conn.LocalAddr and Conn.RemoteAddr methods

check Version field of Bind requests by default