stdenv.mkDerivation: rename meta.evaluates -> meta.available

A much better name.

nixos/doc/manual/default.nix

@@ -36,7 +36,7 @@ let
           package = args.package or (lib.attrByPath path (throw "Invalid package attribute path `${toString path}'") pkgs);
         in "<listitem>"
         + "<para><literal>pkgs.${name} (${package.meta.name})</literal>"
-        + lib.optionalString (!package.meta.evaluates) " <emphasis>[UNAVAILABLE]</emphasis>"
+        + lib.optionalString (!package.meta.available) " <emphasis>[UNAVAILABLE]</emphasis>"
         + ": ${package.meta.description or "???"}.</para>"
         + lib.optionalString (args ? comment) "\n<para>${args.comment}</para>"
         # Lots of `longDescription's break DocBook, so we just wrap them into <programlisting>

pkgs/stdenv/generic/check-meta.nix

@@ -159,7 +159,7 @@ let
     executables = listOf str;
     outputsToInstall = listOf str;
     position = str;
-    evaluates = bool;
+    available = bool;
     repositories = attrsOf str;
     isBuildPythonPackage = platforms;
     schedulingPriority = int;

pkgs/stdenv/generic/make-derivation.nix

@@ -238,9 +238,9 @@ rec {
           position = pos.file + ":" + toString pos.line;
         # Expose the result of the checks for everyone to see.
         } // {
-          evaluates = validity.valid
+          available = validity.valid
                    && (if config.checkMetaRecursively or false
-                       then lib.all (d: d.meta.evaluates or true) references
+                       then lib.all (d: d.meta.available or true) references
                        else true);
         };