bug#20619: 24.5; Pop-up menus clipped on HiDPI (Gtk3/X11)

[Michael Droettboom <mdroe@stsci.edu>]

If in HiDPI mode on Linux [1] the popup menus are constrained to the
upper left quadrant of the screen and are not opened near the mouse
cursor. For example, 'C-mouse-1' in the lower-right hand quadrant opens
an empty menu. 'C-mouse-1' in the upper-right hand quadrant opens a
menu, but not in the correct location.

[1] This mode is set automatically under Gnome, or may get set manually
with:

gsettings set org.gnome.desktop.interface scaling-factor 2

A workaround, which may help to diagnose the bug, is to start emacs
using:

GDK_SCALE=0.5 emacs

Other Gtk3 applications (gnome-terminal, nautilus) so not seem to
exhibit this behavior under the same conditions.



In GNU Emacs 24.5.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.16.2)
of 2015-04-22 on buildhw-08.phx2.fedoraproject.org
Windowing system distributor `Fedora Project', version 11.0.11701000
System Description: Fedora release 23 (Rawhide)

Configured using:
`configure --build=x86_64-redhat-linux-gnu
--host=x86_64-redhat-linux-gnu --program-prefix=
--disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
--bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
--datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
--libexecdir=/usr/libexec --localstatedir=/var
--sharedstatedir=/var/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
--with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk3
--with-gpm=no build_alias=x86_64-redhat-linux-gnu
host_alias=x86_64-redhat-linux-gnu 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
-pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector-strong --param=ssp-buffer-size=4
-grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
-m64 -mtune=generic' LDFLAGS=-Wl,-z,relro'

Important settings:
value of $LC_CTYPE: en_US.utf8
value of $LANG: en_US.utf8
locale-coding-system: utf-8-unix