as requested in LBCLASSIC-184

Within web-applications, it often proves helpful to know the hostname,
request uri and user-agent associated with a given http
request. MDCInsertingServletFilter inserts such data into the MDC.

http://jira.qos.ch/browse/LBCORE-143

stopAndRemoveNow(String key) method was added to AppenderTracker,
allowing immediate removal of a nested appender.

- minor editing of the manual

- the contextName attribute in jmxConfigurator is redundant since the
context name can be set with the <contextName> element. Modified
documentation accordingly. This change was triggered by comments made
by Matthias Kretschmar.

- added paragraph about exemptions in license.html

- making sure that everything compiles under JDK 1.5
- upgraded janino dependency to 2.5.10 from 2.4.3

- testing the error status code emitted by OutputStreamAppender when a layout is set instead of an encoder

ClassicTestConstants.JORAN_INPUT_PREFIX

- added getFile method to ResilientFileOutputStream

- added JNDIBasedContextDiscriminator which should work much better than
ContextBasedtiscriminator.