Changed NAnt build file to use App.config when running nunit tests. Also
removed a trailing semicolon from the tests settings which was causing
problems.

By making NAnt use App.config file, Npgsql tests run either by NAnt
console project file or by running nunit inside IDE (like Xaramrin
Studio) will use the same file and changes will be reflected in both.
Before that NAnt was using different files.

A trailing semicolon in the app settings config for connection string
was making Npgsql throw exceptions about bad formatting.