Changes in version 1.17:

zdiff now creates each FIFO only if needed. Regular uncompressed files are
now opened by diff directly.

zgrep no longer exits prematurely on error when verbosity >= 0.

zgrep now prepends the file name to diagnostics from grep, so that a binary
file that matches or a file causing an error can be identified in recursive
mode.

When processing regular files, the compressors now report the file name
instead of '(stdin)' in diagnostics. To achieve this, the compressors used
with zcat, zcmp, zdiff, and zgrep must meet a new requirement:
When called with the options '-cd' and one file name, they must read
compressed data from the named file and produce decompressed data on the
standard output. (Reported by Daniel Baumann).

As a side effect, calling the compressor with option '-c' saves one call to
fork for regular files. An uncompressed regular file is now directly
connected to the standard input of grep.

ztest now can test non-regular files.

zupdate now rejects an existing non-regular output file instead of trying to
compare it with the input file.

zupdate now passes '-q' to the decompressor if specified.
