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.

Let's add a code comment that says what this tests. For slow020 it tests that dbs are *not* inherited.