Updated chat/ejabberd to 2.1.5.

Short list of changes:
* Erlang/OTP R12 support fixed
* Erlang/OTP R14A support added
* OpenSSL 0.9.8 or higher is required
* BOSH: New optional connection attribute process-delay
* C2S: Don't ask for client certificate when using tls
* C2S: Inform client that SSL session caching is disabled
* CTL: Fix problem when FIREWALL_WINDOW options for erl kernel were used
* CTL: Some systems delete the lock dir; in such case don't use Flock at all
* Caps: Support all the hash functions required by XEP-0115
* Config: Fix typo in --enable-transient_supervisors
* Config: New configure option: --enable-nif
* Extauth: Support parallel script running
* MUC: Allow admins to see private rooms in disco
* ODBC: Correct handling of SQL boolean types
* ODBC: Discard too old queued requests (the caller has already got a timeout)
* ODBC: Fixes wrong SQL escaping when --enable-full-xml is set
* ODBC: Use ets insead of asking supervisor in ejabberd_odbc_sup:get_pids/1
* Pubsub: Enforce disco features results
* S2S: When logging s2s out connection attempt or success, log if TLS is used
* Shared Rosters: When account is deleted, delete also member
  of stored rosters

(fhajny)