Use ${datarootdir} instead of ${datadir} for data files that go
in directories which are shared with other apps. In practical
terms, this doesn't change anything for most users since
${datarootdir} and ${datadir} are the same by default. But this
is useful for distros/OSes which like to store the application
specific files somewhere else then at the root of /usr/share.
Changes to allow this in audacious-plugins will follow.

	modified:   Makefile
	modified:   configure.ac
	modified:   pixmaps/Makefile
	modified:   src/audacious/Makefile
In my previous commit to allow the use of the --with-pkgconfigdir
switch, I inadvertently forgot to update the uninstall target.

	modified:   Makefile