Close session at the end of each unit test so that resources (eg files)
are freed before the next unit test.
QFJ-799 Close sessions after each test case, throw an explicit exception
when session file storesccan't be deleted.
Merge pull request #2 from manureno/master

QFJ-799: SessionTest : Assertion failure as a side effect of previous sessions not being closed
simplify core field manipulations
simplify Message parsing
remove SSLContextFactory double synchronization
improve DefaultMessageFactory:
- try context classloader when loading factory classes if Class.forName fails
- add public addFactory methods for more flexibility
- add version-specific messages modules as optional dependency to bundle imports