Improve error when running without config backend

[Angel Guzman Maeso]

Binary package hint: compiz

I install compiz, but I forget some packages. When I start compiz --replace the terminal show:

libccs: dlopen: /usr/lib/compizconfig/backends/libgconf.so: cannot open shared object file: No such file or directory

I don't know this error, and in the web, don't have much information about solve it.

The solution is install the package compizconfig-backend-gconf (for Gnome) or compizconfig-backend-kconf (for KDE).

This error should be more informative an indicate some information as install this package or so.
In this way, the error would be more user-friendly

[Travis Watkins (amaranth)]

The way the package dependencies are setup the only way you could ever see this error message is if you had enough of compiz not installed to make running compiz at all completely useless so there is no point to changing this error message.