Better detection of truncation in libwandio zlib

Previously, we were returning "success" when reading from a truncated
gzip file and simply returning all bytes that we could successfully
decompress. This is not consistent with other gzip tools, which at least
alert that the file was not complete or the gzip integrity check was missing.

Now we will return an error if we hit an EOF in the gzip stream that is
not immediately preceded by a Z_STREAM_END marker and write an error message
to stderr so the user can know what has occurred.
Handle incomplete file reads in libtrace formats

Some file read function calls assumed that the full amount that was
asked for will be read from the file, which is not necessarily true
especially if the file was truncated.
Fix horrible error reporting in tracestats

The URI seems to get printed about three times in some error messages,
which isn't exactly helpful.