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.

This behavior is now documented for the method and validated with
a unit test.

LOGBACK-818: support for SSL-enabled socket appender and server

LOGBACK-796 RollingFileAppender should have error when File matches FileNamePattern

This commit modifies appenders.html to include information about
SSLSocketAppender, and adds a usingSSL.html (linked from the
relevant sections of appenders.html) that describes the SSL-related
configuration properties.

This commit adds the new appender and modifies the JoranConfigurator
to include rules for SSL configuration types.

This commit adds the new server and modifies SimpleSocketServer so
that its startup logic can also be applied to a SimpleSSLSocketServer.

This commit adds the new appender and modifies the
DefaultNestedComponent rules to include rules for SSL configuration
types.

In addition to the new base appender, this commit includes several
supporting classes that are used to create and configure an
SSLContext and all of its constituent components, and corresponding
unit tests and resources.

added another hsqldb file to gitignore

removed remaining call to new Socket() in reconnect (LOGBACK-815)

Missed one in previous commit.

Patch for LOGBACK-815, LOGBACK-816