util: fix crash converting an invalid future date to string
Post-2038 timestamps cannot be handled on 32-bit architectures. Clamp
such dates to the maximum 32-bit timestamp.
$ "$TESTDIR/hghave" pyflakes || exit 80
$ cd $(dirname $TESTDIR)
$ pyflakes mercurial hgext 2>&1 | $TESTDIR/filterpyflakes.py
mercurial/hgweb/server.py:*: 'activeCount' imported but unused (glob)
mercurial/commands.py:*: 'base85' imported but unused (glob)
mercurial/commands.py:*: 'bdiff' imported but unused (glob)
mercurial/commands.py:*: 'mpatch' imported but unused (glob)
mercurial/commands.py:*: 'osutil' imported but unused (glob)
hgext/inotify/linux/__init__.py:*: 'from _inotify import *' used; unable to detect undefined names (glob)
mercurial/util.py:*: 'from posix import *' used; unable to detect undefined names (glob)
mercurial/windows.py:*: 'from win32 import *' used; unable to detect undefined names (glob)
mercurial/util.py:*: 'from windows import *' used; unable to detect undefined names (glob)