Add enableFallbacks() method.

Author: ctavan

lib/getenv.js

@@ -108,4 +108,8 @@ getenv.disableFallbacks = function() {
   fallbacksDisabled = true;
 };
 
+getenv.enableFallbacks = function() {
+  fallbacksDisabled = false;
+};
+
 module.exports = getenv;

test/fallbacks.js

@@ -10,6 +10,7 @@ tests['getenv.disableFallbacks() makes relying on fallbacks an error'] = functio
   assert.throws(function() {
     getenv.string("url", "http://localhost");
   });
+  getenv.enableFallbacks();
 };