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.

Is this necessary? If query is empty, the main loop won't run and as long as the last code before return doesn't crash (index out of range?), then we don't need a special case.