Use common licence attributes from lib/licenses.nix

Many (less easily automatically converted) old-style strings
remain.

Where there was any possible ambiguity about the exact version or
variant intended, nothing was changed. IANAL, nor a search robot.

Use `with stdenv.lib` wherever it makes sense.

pkgs/development/libraries/libviper/default.nix

@@ -18,9 +18,9 @@ stdenv.mkDerivation rec {
 
   buildInputs = [pkgconfig glib ncurses gpm];
 
-  meta = {
+  meta = with stdenv.lib; {
     homepage = http://libviper.sourceforge.net/;
     description = "Simple window creation and management facilities for the console";
-    license="GPLv2+";
+    license = with licenses; gpl2Plus;
   };
 }