added a function to set the value of an inline edit filed in a review request. 

This is needed in my other review request to allow reviewer suggestions.
https://reviews.reviewboard.org/r/5029/

Opened a review request, clicked on a reviewer suggestion (which triggers a call to appendToFieldValue, ensured that the suggestion was filled into the inline editor. Hit OK and ensured that it was saved in the editor. Did the same with cancel to ensure that it was not remembered.