ZNC 1.6.4

Changes since ZNC 1.6.3

Fixes
=====

* Fixed build with OpenSSL 1.1.
* Fixed build on Cygwin.
* Fixed a segfault after cloning a user. The bug was introduced in ZNC 1.6.0.
* Fixed a segfault when deleting a user or network which is waiting for DNS
  during connection. The bug was introduced in ZNC 1.0.
* Fixed a segfault which could be triggered using alias module.
* Fixed an error in controlpanel module when setting the bindhost of another user.
* Fixed route_replies to not cause client to disconnect by timeout.
* Fixed compatibility with the Gitter IRC bridge.

Internal
========

* Fixed `OnInvite` for modpython and modperl.
* Fixed external location of GoogleTest for `make test`.