add tests for charset parameter on live connection

The charset parameter is only tested in the dsn parser.
Add tests on the database connection.
This is currently broken for fallback charsets.
fix fallback charset handling

test if the fallback is set, do not rely on error code
minor typo fix
throw error if no charset could be set
Merge pull request #43 from arnehormann/master

add tests for charset parameter on live connection