(minor) standardized error messages

Author: cloudhead

lib/vows.js

@@ -128,7 +128,7 @@ function addVow(/* description & callback */) {
     } else if (args[0].callback && args[0].context) {
         vow = args[0];
     } else {
-        throw new(Error)("wrong argument type for addVow()");
+        throw new(Error)("wrong argument type for addVow().");
     }
 
     return this.addListener("success", function () {
@@ -221,7 +221,7 @@ function addVows(tests) {
 
     if (typeof(tests) === 'object') {
         if ('topic' in tests) {
-            throw new(Error)("Missing top-level context.");
+            throw new(Error)("missing top-level context.");
         }
         // Count the number of vows/promises expected to fire,
         // so we know when the tests are over.