Inlude stack trace of connector exception in log message produce with ERROR level. Don't do it anymore under DEBUG level only. Update unit test and confirm fix with an "upgraded" 6.4.0 version (community edition)
Fixed Java version required to build Engine in README.md file
Revert modification about Java version required to compile Engine as it still possible to use Java 6
Merge pull request #4 from amottier/6.4.x

Inlude stack trace of connector exception in log message