v0.6.1

This is a minor, but recommended, bugfix release. This is the last version of BrowserFS to officially support IE9. IE8 may also work in this release, but it is untested.

• The XmlHttpRequest file system no longer throws an exception during certain synchronous downloads. Sometimes, a synchronous download would throw an exception because we would try to write a large value into a buffer as an 8-bit unsigned integer without disabling range checking. We now properly disable range checking, as we expect these values to be clamped to 8 bits.
• AsyncMirror can now be used with synchronous file systems. Previously, we threw an exception whenever someone tried to mirror a synchronous file system. However, there are some cases where this is desired -- e.g., mirroring an XmlHttpRequest file system to avoid synchronous XHR on the main thread.