Add explicit ext-curl dependency

Author: Francesco Abeni

composer.json

@@ -12,7 +12,8 @@
   ],
   "require": {
     "php"                     : ">=5.3.2",
-    "symfony/http-foundation" : "~2.0"
+    "symfony/http-foundation" : "~2.0",
+    "ext-curl"                : "*"
   },
   "require-dev": {
     "sami/sami"               : "dev-master"