outdated: optimize out an extra HTTP request

While the request to foo/latest will be less data over the wire,
it's also much less likely to be cached by the registry CDN.

This, it's more likely to be a trip to the origin server, which is
much slower than serving out of the CDN.

Additionally, we can then use that data object to check the
versions hash here in outdated.js, rather than doing a full tgz
download and unpack for 'cache.add'.

lib/outdated.js

@@ -29,6 +29,7 @@ var path = require("path")
   , color = require("ansicolors")
   , styles = require("ansistyles")
   , table = require("text-table")
+  , semver = require("semver")
 
 function outdated (args, silent, cb) {
   if (typeof cb !== "function") cb = silent, silent = false
@@ -222,10 +223,33 @@ function shouldUpdate (args, dir, dep, has, req, depth, cb) {
 
   var registry = npm.registry
   // search for the latest package
-  registry.get(dep + "/latest", function (er, l) {
+  registry.get(dep, function (er, d) {
     if (er) return cb()
-    // so, we can conceivably update this.  find out if we need to.
-    cache.add(dep, req, function (er, d) {
+    if (!d || !d['dist-tags'] || !d.versions) return cb()
+    var l = d.versions[d['dist-tags'].latest]
+    if (!l) return cb()
+
+    // set to true if found in doc
+    var found = false
+
+    var r = req
+    if (d['dist-tags'][req])
+      r = d['dist-tags'][req]
+
+    if (semver.validRange(r, true)) {
+      // some kind of semver range.
+      // see if it's in the doc.
+      var vers = Object.keys(d.versions)
+      var v = semver.maxSatisfying(vers, r, true)
+      if (v) {
+        return onCacheAdd(null, d.versions[v])
+      }
+    }
+
+    // We didn't find the version in the doc.  See if cache can find it.
+    cache.add(dep, req, onCacheAdd)
+
+    function onCacheAdd(er, d) {
       // if this fails, then it means we can't update this thing.
       // it's probably a thing that isn't published.
       if (er) {
@@ -247,6 +271,7 @@ function shouldUpdate (args, dir, dep, has, req, depth, cb) {
         doIt(d.version, l.version)
       else
         skip()
-    })
+    }
+
   })
 }