Don't relink things that are already linked right

lib/utils/link.js

@@ -12,7 +12,17 @@ var fs = require("graceful-fs")
 function linkIfExists (from, to, gently, cb) {
   fs.stat(from, function (er) {
     if (er) return cb()
-    link(from, to, gently, cb)
+    fs.readlink(to, function (er, fromOnDisk) {
+      // if the link already exists and matches what we would do,
+      // we don't need to do anything
+      if (!er) {
+        var toDir = path.dirname(to)
+        var absoluteFrom = path.resolve(toDir, from)
+        var absoluteFromOnDisk = path.resolve(toDir, fromOnDisk)
+        if (absoluteFrom === absoluteFromOnDisk) return cb()
+      }
+      link(from, to, gently, cb)
+    })
   })
 }