Ticket #4272: nc.ext: fix recognition of plain and compressed man pages.

Ticket #4272: nc.ext: fix recognition of plain and compressed man pages.

Support various versions of file utility which output is changed from
one version to another:

$ file --version
file-4.26
magic file from /etc/magic:/usr/share/file/magic
$ file mc.1
mc.1: ASCII troff or preprocessor input text
$ file -z -L mc.1.gz
mc.1.gz: ASCII troff or preprocessor input text (gzip compressed data, was "mc.1", last modified: Tue Aug 24 08:17:47 2021, from Unix)

$ file --version
file-5.40
magic file from /etc/file/magic
eccomp support included
$ file mc.1
mc.1: troff or preprocessor input, ASCII text
$ file -z -L -S mc.1.gz
mc.1.gz: troff or preprocessor input, ASCII text (gzip compressed data, was "mc.1", last modified: Wed Aug 18 04:41:29 2021, from Unix)

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>