No longer support setting the statistics_log path in WT_CONNECTION::reconfigure.
No longer support setting a custom name for statistics files, only allow a destination directory.
Be more explicit about which logging configuration options are allowed in WT_CONNECTION::reconfigure.
The aim of these changes is to avoid situations where applications that embed WiredTiger allow their users to overwrite unexpected files on a file system.
This potentially requires an upgrade step for applications that were specifying a non-standard file name component for statistics log file names, it's not backward compatible.