Since we have to use pkill, kludgily, for the right combination of
portability and featurefulness, put the code in one place rather than
duplicating it everywhere.
https://bugzilla.gnome.org/show_bug.cgi?id=635089
Add Util.spawn, Util.spawnCommandLine, and Util.spawnDesktop for
spawning a command/argv/.desktop file in the background, automatically
handling errors via MessageTray.SystemNotificationSource(), and
Util.trySpawn, Util.trySpawnCommandLine, and Utils.trySpawnDesktop
that don't do automatic error handling (but do at least clean up the
error message in the exception a bit).
Update various other bits of code around the shell to use the new
methods.
https://bugzilla.gnome.org/show_bug.cgi?id=635089
Rename imports.misc.utils to imports.misc.util for more consistency
(eg, with shell-util).
Also, use the string-based RegExp() constructor rather than a RegExp
literal, since the literal is extremely difficult to parse correctly,
and confuses emacs and probably other editors and thus messes up
autoindentation, etc.
https://bugzilla.gnome.org/show_bug.cgi?id=635089
