To compile user defined functions, the javax.tools.JavaCompiler is now used if available, and no temporary files are created.

inline the "create temporary LOBs" methods into the constructor so that I can make more fields final

re-organise LobStorageBackend code a little, so we don't need to correct the precision of a CLOB later on

Simplify the code and only store DataHandler.

- fix an occasional error in the test-case

Query Statistics: new feature which stores the newest 100 SQL queries executed and their performance data.
Useful for tracking down badly performing queries.