Added missing unsafeMethods.txt (seems somehow it was gone during SVN to GIT migration)
Restored whitespaces to be like in the SVN to make merges easier.
Merge from 2.3 SVN: (Just some JavaDoc fixes.)
Merge from 2.3 SVN: Making ConcurrentMapFactory available everywhere from within FreeMarker. Also improving it a bit.
Merge from 2.3 SVN: BeansWrapper introspection cache improvements:
- Improved multi-core performance:
  - Use ConcurrentHashMap if available
  - Don't block while introspecting a newly discovered class
  - If multiple threads need to introspect the same newly discovered class, only one of them will do it, the others will wait for its result
- Refactoring to prevent deadlocking oversights in the future
- Added public API for clearing the class cache
- Some cleanup in internal code structuring and naming