adjust override behaviour

lib/config.js

@@ -31,22 +31,19 @@ var asp = require('rsvp').denodeify;
 exports.derivePackageConfig = function(pjson, override) {
   var dpjson = extend({}, pjson);
 
-  // apply the jspm internal overrides first
-  if (pjson.jspm) {
-    extend(dpjson, pjson.jspm);
+  // first derive the override
+  dpjson.jspm = extend({}, pjson.jspm || {});
 
-    if (pjson.jspm.dependencies)
-      dpjson.registry = dpjson.registry || 'jspm';
-  }
+  if (override)
+    extend(dpjson.jspm, override);
 
-  if (override) {
-    extend(dpjson, override);
+  // then apply the override
+  extend(dpjson, dpjson.jspm);
 
-    if (override.dependencies)
-      dpjson.registry = dpjson.registry || 'jspm';
-  }
+  // add default registry option if dependency override provided
+  if (dpjson.jspm.dependencies)
+    dpjson.registry = dpjson.registry || 'jspm';
 
-  // finally set the derived package.json as the "jspm" property on the package.json
   return dpjson;
 }