GUAC-904: Implement copy constructor for GuacamoleConfiguration.
GUAC-906: Implement GuacamoleConnectionClosedException. Throw when read/write fails due to closure.
GUAC-909: Log "unsupported operation" exceptions at debug level.
GUAC-909: Log full exceptions only in debug level. Rephrase log messages.
GUAC-908: Handle errors during connect/bind/query distinctly. Only rethrow server error if connection or query fails - failure to bind is just an invalid login.
GUAC-907: Log source address, using X-Forwarded-For if available (after validation).
GUAC-434: Allow SimpleUserContext/SimpleAuthenticationProvider to provide actual usernames.
Merge branch 'master' into GUAC-546

Conflicts:
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/AuthenticatingFilter.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/RestrictedHttpServlet.java
	guacamole/src/main/java/org/glyptodon/guacamole/net/basic/TunnelModule.java