This is a stopgap solution suggested by minherz@ in #747. The long-term fix is #32 but that seems like it could take some time (it's been open 3 years and is pending a major version bump).

This enables us to enhance the c.g.cloud.logging.LogEntry in ways that require access to the original java.util.logging.LogRecord, e.g.:

• Setting SourceLocation using extra, more accurate context the Google Flogger library captures (on a subclass of the JUL LogRecord),
• Recording logRecord.getThreadID,
• Recording exception name explicitly from record.getThrown(),
• etc