posix: don't compare atime when determining if a file has changed
A file's atime might change even if the file itself doesn't change. This might
cause us to invalidate caches more often than necessary.
Before this change, hg add often resulted in the dirstate being parsed twice
on systems that track atime. After this change, it is only parsed once. For a
repository with over 180,000 files, this speeds up hg add from 1.2 seconds to
1.0.
Test document extraction
$ "$TESTDIR/hghave" docutils || exit 80
$ HGENCODING=UTF-8
$ export HGENCODING
$ { echo C; find "$TESTDIR/../i18n" -name "*.po" | sort; } | while read PO; do
> LOCALE=`basename "$PO" .po`
> echo
> echo "% extracting documentation from $LOCALE"
> echo ".. -*- coding: utf-8 -*-" > gendoc-$LOCALE.txt
> echo "" >> gendoc-$LOCALE.txt
> LC_ALL=$LOCALE python "$TESTDIR/../doc/gendoc.py" >> gendoc-$LOCALE.txt 2> /dev/null || exit
>
> # We call runrst without adding "--halt warning" to make it report
> # all errors instead of stopping on the first one.
> echo "checking for parse errors"
> python "$TESTDIR/../doc/runrst" html gendoc-$LOCALE.txt /dev/null
> done
% extracting documentation from C
checking for parse errors
% extracting documentation from da
checking for parse errors
% extracting documentation from de
checking for parse errors
% extracting documentation from el
checking for parse errors
% extracting documentation from fr
checking for parse errors
% extracting documentation from it
checking for parse errors
% extracting documentation from ja
checking for parse errors
% extracting documentation from pt_BR
checking for parse errors
% extracting documentation from ro
checking for parse errors
% extracting documentation from ru
checking for parse errors
% extracting documentation from sv
checking for parse errors
% extracting documentation from zh_CN
checking for parse errors
% extracting documentation from zh_TW
checking for parse errors