[MPRIS] Change to DesktopEntry

[Alex Merry]

I propose a change to the wording of the DesktopEntry property which
will not affect most media players.

tl;dr: DesktopEntry should return the path (minus .desktop) relative to
$XDG_DATA_DIRS/applications, not the basename of the file.



Currently, it says that Desktop Entry should be:

> The basename of an installed .desktop file which complies with the Desktop entry specification, with the ".desktop" extension stripped.
> 
> Example: The desktop entry file is "/usr/share/applications/vlc.desktop", and this property contains "vlc"

KDE4 applications install their desktop files in
$DATA_DIR/applications/kde4/<something>.desktop.  Following what the
spec says would mean returning "<something>".

In practise, they currently return "kde4-<something>", which is
something akin to the XDG applications menu spec's desktop file ID.

GIO's g_desktop_app_info_new() function deals with this fine, but it's
not so easy in KDE, Qt or, I expect, elsewhere.  There, you want to pass
in "kde4/<something>.desktop" (note that simply replacing '-' with '/'
on the client side won't do; <something> could contain hyphens).

So, I suggest that they should be returning "kde4/<something>", and the
spec should reflect that by saying something like

> The path (relative to $XDG_DATA_DIRS/applications) of an installed .desktop file which complies with the Desktop entry specification, with the ".desktop" extension stripped.
> 
> Example: If the desktop entry file is "/usr/share/applications/vlc.desktop", then this property contains "vlc"; if the desktop entry file is "/usr/share/applications/kde4/amarok.desktop", then this property contains "kde4/amarok".

This would just be a correction/clarification/change to the existing
spec, rather than a new spec version.

Thoughts?  Objections?

Alex