(#1068) - cache websql dbs

Safari 7 starts throwing DOM Exception 11 if
we open up too many db handles, which crashes
our unit tests. Caching them fixes that.

lib/adapters/websql.js

@@ -7,6 +7,8 @@ function quote(str) {
   return "'" + str + "'";
 }
 
+var cachedDbs = {};
+
 var openDB = utils.getArguments(function (args) {
   if (typeof global !== 'undefined') {
     if (global.navigator && global.navigator.sqlitePlugin &&
@@ -17,7 +19,11 @@ var openDB = utils.getArguments(function (args) {
       return global.sqlitePlugin.openDatabase
         .apply(global.sqlitePlugin, args);
     } else {
-      return global.openDatabase.apply(global, args);
+      var db = cachedDbs[args[0]];
+      if (!db) {
+        db = cachedDbs[args[0]] = global.openDatabase.apply(global, args);
+      }
+      return db;
     }
   }
 });