bug#24823: 25.1.50; parse-time-string cannot parse ISO 8601 time string

[Hong Xu]

In GNU Emacs 25.1.50.8 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
Repository revision: 91c97b6eed708f5a1f34478b52f42ef9e51efcb5
Windowing system distributor 'The X.Org Foundation', version 11.0.11604000
System Description:     Debian GNU/Linux 8.6 (jessie)

Configured using:
 'configure --with-xwidgets --with-modules
 --prefix=/home/hong/.local/opt/emacs'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES XWIDGETS

Important settings:
  value of $LC_CTYPE: zh_CN.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=fcitx
  locale-coding-system: utf-8-unix

The function parse-time-string cannot parse ISO 8601 time string, e.g.,
2005-04-07T22:13:13, which is pretty ubiquitous nowadays.
(parse-time-string 2005-04-07T22:13:13) returns a list full of nils.

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