Captialize meta.description of all packages

In line with the Nixpkgs manual.

A mechanical change, done with this command:

  find pkgs -name "*.nix" | \
      while read f; do \
          sed -e 's/description\s*=\s*"\([a-z]\)/description = "\u\1/' -i "$f"; \
      done

I manually skipped some:

* Descriptions starting with an abbreviation, a user name or package name
* Frequently generated expressions (haskell-packages.nix)

pkgs/tools/backup/partimage/default.nix

@@ -26,7 +26,7 @@ stdenv.mkDerivation {
   ];
 
   meta = {
-    description = "opensource disk backup software";
+    description = "Opensource disk backup software";
     homepage = http://www.partimage.org;
     license = stdenv.lib.licenses.gpl2;
     maintainers = [stdenv.lib.maintainers.marcweber];