AppendFile ensures that it appends the entire buffer. Returns
an error otherwise, this patch removes the necessity for the
caller to look for 'n' return on short writes.
Ref #1893
This patch brings in the removal of debug logging altogether, instead
we bring in the functionality of being able to trace the errors properly
pointing back to the origination of the problem.
To enable tracing you need to enable "MINIO_TRACE" set to "1" or "true"
environment variable which would print back traces whenever there is an
error which is unhandled or at the handler layer.
By default this tracing is turned off and only user level logging is
provided.
