Fix a few issues with TRACE2 output

[mjcheetham]

I noticed a few problems with the TRACE2 support when writing to a pipe/socket. The handling of the trace2.eventTarget setting to get the correct pipe name/socket file path was incorrect resulting in names like "pipe\foobar" when given "//./pipe/foobar" on Windows, when it should be "foobar".

Also the event field name 'format' is incorrect; it should be 'fmt'.