More description fixes

* Remove package name
* Start with upper case letter
* Remove trailing period

Also reword some descriptions and move some long descriptions to
longDescription.

I'm not touching generated packages.

pkgs/misc/emulators/hatari/default.nix

@@ -15,7 +15,7 @@ stdenv.mkDerivation rec {
 
   meta = {
     homepage = "http://hatari.tuxfamily.org/";
-    description = "Hatari is an Atari ST/STE/TT/Falcon emulator.";
+    description = "Atari ST/STE/TT/Falcon emulator";
     license = "GPLv2+";
     platforms = with stdenv.lib.platforms; all;
   };

pkgs/misc/screensavers/xlockmore/default.nix

@@ -39,7 +39,7 @@ stdenv.mkDerivation rec {
     + (if pam != null then " --enable-pam --enable-bad-pam" else " --disable-pam");
 
   meta = {
-    description = "Xlockmore, a screen locker for the X Window System.";
+    description = "Screen locker for the X Window System";
     homepage = "http://www.tux.org/~bagleyd/xlockmore.html";
     license = "GPL";
   };