Review Board 3.0 shipped with a faster, more condensed method for

streaming diff fragments for comments, which stored information on the

comment and the payload of the text. It also introduced a similar format

for sending updates to the review request page. These payloads sent

Unicode strings, prefixing them with byte lengths, so that the client

could read out the appropriate number of bytes for each string. However,

this didn't actually work in JavaScript, since the entire payload was

interpreted as a JavaScript string, meaning that byte counts didn't

matter. A follow-up change attempted to fix this, but didn't support

Emoji characters.
This redoes the entire mechanism to fetch actual binary data and to

parse that data properly, only converting data to strings when needed.

To do this, a jQuery Ajax transport was added that enables use of

XMLHttpRequest2's arraybuffer and blob types. This transport was

designed to follow the basic logic of the standard transport, but

doesn't include some of the more specialized features that we don't

need. This effectively limits IE support to 10 and higher, but IE9

already fails many tests for Review Board 3.0.
Some of the data that was previously sent over as strings containing an

integer and a newline delimiter has been changed to send packed 32-bit

integers instead, reducing both the size of the data and the work

required by the parser.
Down the road, these improvements will let us send other forms of binary

data, such as images or documents, in other similar transfer systems.

Unit tests pass in Chrome, Firefox, Safari, IE10/11, and Edge.
Manually tested both diff fragments and review request updates (with

Unicode/Emoji).