bug#25747: 25.1.91; hideshow binding C-c @ C-h overrides help

[Allen Li]

hideshow-minor-mode binds C-c @ C-h, preventing C-h from being used as
the help key to describe the bindings under the C-c @ prefix.

In GNU Emacs 25.1.91.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.8),
modified by Debian
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description: Ubuntu 14.04 LTS

Configured using:
 'configure --build x86_64-linux-gnu --build x86_64-linux-gnu
 --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/google-emacs:/etc/emacs:/usr/local/share/emacs/25.1.91+gg1+2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1.91+gg1+2/site-lisp:/usr/share/emacs/site-lisp
 --with-crt-dir=/usr/lib/x86_64-linux-gnu --disable-build-details
 --disable-silent-rules --with-modules GOOGLE_VERSION=25.1.91+gg1+2
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 build_alias=x86_64-linux-gnu 'CFLAGS=-g -O2 -fstack-protector
 --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro
 -Wl,-fuse-ld=gold,--export-dynamic-symbol=__google_auxv'
 'CPPFLAGS=-D_FORTIFY_SOURCE=2 -DGOOGLE_EMACS_DEFINE_AUXV''

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