Make IndexedDB work with web workers on Chrome

[terrycojones]

Web workers do not have access to the window object, so these lines do not work for finding the IndexedDB API

        fullproof.store.indexedDB =  window.indexedDB || window.webkitIndexedDB || window.mozIndexedDB || window.msIndexedDB;
        fullproof.store.IDBTransaction = window.IDBTransaction || window.webkitIDBTransaction || window.mozIDBTransaction || window.msIDBTransaction || {};

fortunately, on Chrome at least, indexedDB and IDBTransaction are both present in the global scope, so there is a trivial fix (coming up in a pull request).