Log Message:
Update ejabberd to 2.1.13.

Bugs fixed since 2.1.12:
* Compilation: Detect correctly newer Darwin versions (EJAB-1594)
* Guide: ejabberd_service expects a shaper_rule, not a shaper
* MUC: Handle multiple < and > in mod_muc_log plaintext mode (EJAB-1640)
* MUC: Handle ~ control sequence in text of mod_muc_log (EJAB-1639)
* MUC: list_to_integer/2 only works in OTP R14 and newer
* Pubsub: access_createnode acl also applies to auto created nodes
* Web: Normalize HTTP path