Better error message on engine mismatch

lib/cache.js

@@ -410,10 +410,19 @@ function addNameRange (name, range, cb) {
 }
 
 function installTargetsError (requested, data) {
-  return new Error("Not found: "+data.name+"@'"+requested+"'\n"
-                  +"Valid install targets:\n"
-                  +JSON.stringify(Object.keys(data["dist-tags"])
-                          .concat(Object.keys(data.versions || {}))))
+  var targets = Object.keys(data["dist-tags"]).filter(function (f) {
+    return (data.versions || {}).hasOwnProperty(f)
+  }).concat(Object.keys(data.versions || {}))
+
+  requested = data.name + (requested ? "@'" + requested + "'" : "")
+
+  targets = targets.length
+          ? "Valid install targets:\n" + JSON.stringify(targets)
+          : "No valid targets found.\n"
+          + "Perhaps not compatible with your version of node?"
+
+  return new Error( "No compatible version found: "
+                  + requested + "\n" + targets)
 }
 
 function addNameVersion (name, ver, cb) {