r7747: - simplified the ldap server buffer handling

r7747: - simplified the ldap server buffer handling

- got rid of the special cases for sasl buffers

- added a tls_socket_pending() call to determine how much data is waiting on a tls connection

- removed the attempt at async handling of ldap calls. The buffers/sockets are all async, but the calls themselves
  are sync.
(This used to be commit 73cb4aad229d08e17e22d5792580bd43a61b142a)