taskbar: add option to close all windows within a group
taskbar: only close windows on same desktop

This is so as to only close those tasks that would be shown by a
left-click.
plugins: assign PluginClass in a C99 compatible fashion

That is, without using the GNUism that allows a colon between structure
member name and value, but rather in the standard C99 style.
Basic Multimonitor support - ID: 3397801

I have implemented basic multi-monitor support for lxpanel. It still
only supports one GdkScreen instance. It uses gdk_screen_get_n_monitors
and related functions. Every panel now has an associated monitor, and
the task bar has an option to only show tasks from the same monitor.

Here is what my desktop looks like with it:
http://img684.imageshack.us/img684/825/dualb.jpg

This was mainly for my own convenience so the panel settings interface
was only partially updated (It no longer checks for overlapping panels).
Since this is my first time contributing to an open-source project, I
want to see what it's thought of, before considering investing any more
time into it.
batt: put tooltip generation in separate function

This way it will be easier to incorporate more information in the
tooltip.
batt: display some more information in the tooltip
batt: make showing extended information configurable
Introduce 'spawn_command_async()', with error reporting

This should clarify bugs such as ID 3614887,
https://sourceforge.net/tracker/?func=detail&atid=894869&aid=3614887&group_id=180858
menu: Add accelerators to Main menu - ID: 3607870

With this patch we can add a underscore (_) before the letter we want to
use as accelerator on Name of Desktop Entry section.

Please see Feature Request 3592406.
src/panel: update copyright
configurator: use less casting

The GTK_*() functions/macros can have checks in them.
lxpanel_launch_app(): allow starting in a different workdir

Should fix bug ID 3598840,
https://sourceforge.net/tracker/?func=detail&atid=894869&aid=3598840&group_id=180858
Version 0.6.1, release!
Merge branch 'next-gtk2'

Conflicts:
	src/plugins/volumealsa/volumealsa.c