PCT-1085

Fixes for slow log parser.
For PCT-1085 & PCT-1006
- Empty queries are not being sent in the response.
- Cheked "use", "uSe", etc
- Checked dbname in use between backticks.
- More than one "use statement" in a slow log file.
- Empty queries are not being processed by the fingerprinter.

This tests that `use` with a back-tick quoted db works.