Release 0.9.3:
-PLAIN mechanism is used only when no other mechanisms are supported
-Legacy authentication is disabled by default, can be enabled with connection flag
 XMPP_CONN_FLAG_LEGACY_AUTH
-Session is not established if it is optional
-Fixed a bug causing a reused connection not to cleanup properly
-Improved debug logging in OpenSSL module
-Few memory leaks fixed

Also fix some build flag

Signed-off-by: Chih-Wei Chen <changeway@gmail.com>