SQL Logger should log the last failed query

The SQL Logger is only called after a query has been executed (this was changed to allow profiling of the queries). This makes it difficult to determine which query has failed.

The commit that changed the functionality is at: http://github.com/doctrine/dbal/commit/fe0f0e4b8c6c5308cab3d683c552f61317de7067

It seems that the logger interface needs to be changed to two functions, a pre-query function and a post-query function. Profiling should be handled by the logger if it chooses and not by the connection class.