Blocking Calls on versionTransactions

[axemclion]

Version transactions are not blocking, they should not allow any other transactions when version transactions are in progress

[brettz9]

Will really need to be handled along with #273 .

[brettz9]

For single processes, this issue is now fixed in master and passing a number of formerly failing tests.

However, I think we should keep this issue open as blocked/versionchange events still don't work if someone is running multiple tabs or processes

In the browser, this fix might be implemented via a shared worker but if a browser supports that, it might not be in much need of an IndexedDB shim.

In Node, this fix might be implemented via a shared process or such (ideally via a SharedWorker polyfill which we need for testing anyways).

As mentioned, #273 is another issue relating to multiple processes which ought to be addressed.

[brettz9]

However, I'll relabel the issue as environment-specific since it probably isn't really practical to polyfill for the browser but it could be and ideally will be done in Node.