Fix for IE8 Content Type Request Header

IE8 sends requests where the accepted content types are not separated by commas, but by commas followed by spaces. I adjusted the regular expression used for splitting the content types to account for this. Without this fix, requests for a soy-template driven web page coming from an IE8 fail with a server error (500) when the webapp runs locally.

Change-Id: Ib60c13dfb3bb7009abeef09de237daf5812143f5