[Bug-tar] Warning message when reading partial blocks from stdin.

[Laurence Bond]

Problem:
We have some generic script code which runs on multiple
platforms. Consequently it has to work with tar utilities
besides GNU tar.

On GNU Tar versions 1.14, 1.15 & 1.15.1, we get a warning out
about partial block reads eg

gzip -d -c a_tar_file.tar.gz | tar tvf - > /dev/null
gtar: Read 9216 bytes from -

No other tar utility we use generates this warning including earlier
versions of GNU tar. I recognise that this example could be recast
into a GNU specific form. However the issue is little bit more general
than decompression as the code in src/buffer.c seems to apply to any
input stream other than one created by tar for used with a decompression
tool.

The warning seems to be unnecessary. The fact it cannot be disabled is
alarming. Redirecting to stderr to /dev/null may mean genuine errors
or warnings are missed.


                                Laurence Bond