Bugfixes.

* src/buffer.c (try_new_volume): Print more information with error
diagnostics.
(_gnu_flush_write): Improve error checking.  Adjust
real_s_sizeleft before calling new_volume to avoid creating
malformed multivolume headers.
* tests/delete05.at, tests/gzip.at, tests/ignfail.at,
tests/longv7.at, tests/lustar01.at, tests/lustar02.at,
tests/shortfile.at: Update to match new diagnostic wording
(see 2008-05-06).

* NEWS: Update.