Steps to reproduce:
1. With autocompletion turned on, attempt to add a contact to an email
in any "sender" field (i.e. To:, CC:, BCC:, etc.) or to a meeting notice
such that a GAL lookup is attempted.
2. 


Stack trace:
stack trace when it gets a SIGPIPE on the LDAP connection
---------------------------------------------------------
Program received signal SIGPIPE, Broken pipe.

+ Trace 60144

Other information:
The bug happens when the GC server times out the LDAP connection and then
connector reconnects. (On his server, this happens after the LDAP connection
is idle for 10 minutes, which you can tell by doing "netstat --inet -n |
grep 3268" and waiting for the socket to change from ESTABLISHED to CLOSE_WAIT.)

From looking at the two traces, the problem seems to be that one thread calls
gal_reconnect() while another thread is using the LDAP connection. So we need
to protect bl->priv->ldap with a mutex to keep that from happening.