Didn't seem to do anything and was producing a lot of warnings

Same fix as in:
http://git.xfce.org/users/eric/xfce4-power-manager/commit/?h=gtk3&id=4329d2601a35ccd2a48a509d9027b3a5707b3e4b

Seems like creating/destroying menus leaks memory.

GdkEvent coordinates should be refer to GdkWindow and indeed
in Gtk3.14 that is the case so no extra translation is needed.
However, in Gtk3.12, the coordinates refer to the slider widget,
even though it has no GdkWindow associated with it.
TBC if there is a better way of handling this, but Gtk version
checking works well.

This change was ported from libido upstream:
http://bazaar.launchpad.net/~indicator-applet-developers/ido/trunk.15.04/revision/187

Since symbolic icons are usually only 16px, the size steps
help to keep the icon sharp.

based on the widget's padding and border instead of
an relying on an arbitrary value.

(gtk_image_menu_item deprecation warning to be ignored)

Create README and NEWS contents.
Improve description.
Update author information.

Make the default mixer command a compile-time option and rename mixer
name to mixer command since it is interpreted a command which can be
optionally specified with full path and command line options.

Use xfce4-panel debuging methods described on
http://docs.xfce.org/xfce/xfce4-panel/debugging#debugging_plugins.
In particular log to stderr and enable debug logging if the PANEL_DEBUG
environment variable is set to "all".
Change G_LOG_DOMAIN to the more intuitive pulseaudio-plugin.
Remove logging to a logfile as multiple plugin instances clobber the
logfile and automatic restart after abort() or crash truncates the
file.
Use pulseaudio_plugin_debug instead of g_debug which provides
additional information.

Conflicts:
	panel-plugin/pulseaudio-plugin.c

(Harald Judt)

Wired up a "mixer-name" property.

Commented out lines demonstrate the issue with libintl setup:
- compilation warning (implicit _() definition)
- runtime crash (no '_' symbol)

Forgot to add them in the previous commit.