Add some primops to lib

lib/trivial.nix

@@ -16,7 +16,7 @@ rec {
   or = x: y: x || y;
   and = x: y: x && y;
   mergeAttrs = x: y: x // y;
-  
+
   # Take a function and evaluate it with its own returned value.
   fix = f: let result = f result; in result;
 
@@ -26,7 +26,7 @@ rec {
   # `seq x y' evaluates x, then returns y.  That is, it forces strict
   # evaluation of its first argument.
   seq = x: y: if x == null then y else y;
-  
+
   # Like `seq', but recurses into lists and attribute sets to force evaluation
   # of all list elements/attributes.
   deepSeq = x: y:
@@ -35,4 +35,10 @@ rec {
     else if builtins.isAttrs x
       then deepSeqAttrs x y
       else seq x y;
+
+  # Pull in some builtins not included elsewhere.
+  inherit (builtins)
+    pathExists readFile isBool isFunction
+    isInt add sub lessThan;
+
 }