renamed SSL configuration mocks to be consistent with base class names
ensure that SSLConfiguration.getParameters() never returns null

This behavior is now documented for the method and validated with
a unit test.
added MockContextAware to allow testing of informational messages
fixed content of an informational message
added unit tests for SSLContextFactoryBean
fixed a potential NPE in SSLSocketAppenderBase

If the appender configuration did not specify an SSL configuration, an
NPE would occur in method start when creating the SSLContext.  This NPE
would be trapped and logged, but subsequently the getSocketFactory
method would be called and would return null, potentially causing an NPE
further up the stack.  The fix is to ensure that the appender always has
a default SSL configuration, even if one is not specified in the Joran
configuration.

Unit tests for the SSLConfiguration already validate that an SSLContext
can be successfully created from an SSLConfiguration that is merely
instantiated, but has none of its properties configured.
added missing class header doc comments
improved doc comment for getSocketFactory method
initialize SocketServer.port to default used by SocketAppenderBase

The DEFAULT_PORT defined in SocketAppenderBase needed a public modifier
to allow it to be referenced in SocketServer.
Merge branch 'potentialNPEInSSLSocketAppenderBase' into LOGBACK-819
improved error logging in StreamClient

This should make it easier to diagnose SSL negotiation problems, in
particular.