* doc/autoconf.texi: Be more consistent about using @acronym with

* doc/autoconf.texi: Be more consistent about using @acronym with
"HP" and "HP-UX".  Remove mention of OSF; the old version wasn't
quite right (it talked about "OSF/Tru64", even though the
operating systems were called OSF/1, Digital UNIX, and Tru64 UNIX,
and it even mentioned "OSF 4"!) and at this point there's little
reason to talk about OSF any more, since it died in 1994.
(Specific Compiler Characteristics): Simplify example of
negative-size array.
(File Descriptors): Reorder to make the text flow better.
Remove joke about "appreciate the various levels"; I didn't get it.
Add remark about HP-UX sh -x bug with stderr noted by Bob Proulx in
<http://lists.gnu.org/archive/html/bug-coreutils/2006-06/msg00225.html>.
(File Descriptors, Limitations of Usual Tools):
Tone down the advice against renaming or removing open files.
(Limitations of Usual Tools): Add a new section, on 'rm'.