Manual pages: order ENVIRONMENT / FILES / CONFORMING TO consistently

Manual pages: order ENVIRONMENT / FILES / CONFORMING TO consistently

There is value in ensuring that manual page sections use consistently
named sections, as far as possible, and also that sections have a
consistent order within manual pages. This is one of a series of patches
to place manual page sections in a consistent order.

In this patch, we ensure that the ENVIRONMENT, FILES, and CONFORMING TO
sections are always placed toward the end of the page, just above NOTES.

One page is not fixed by this patch: term-utils/agetty.8. This page
is a mess of unusual section names, and probably requires an individual
edit.

Testing that no gross editing mistake (causing accidental loss or addition
of text) was performed as follows:

    $ cat $(grep '\.SH' -l $(find . -name '*.[1-9]') |sort) | sort > a
    [Apply patch]
    $ cat $(grep '\.SH' -l $(find . -name '*.[1-9]') |sort) | sort > b
    $ diff a b
    $ echo $?
    0

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>