Method StringBuilder.AppendFormat(string,Object,Object) is available in Mono and .NET 4.5 but not in .NET for Windows Phone 8. This causes app built with this method to fail.

Steps to reproduce:
1. Create a new WP8 project
2. Create a script, make a use of StringBuilder.AppendFormat(string,Object,Object) method
3. Deploy it to a Windows Phone 8 device.
4. Either Unity 4.3 will throw a reference rewriter exception while building or Unity 4.2 player will throw InnerException

Expected result: Unity should use function with comma separated list of Object arguments - StringBuilder.AppendFormat(string,params Object[])

Reproduced with:
Version 4.2.0b5 (8959c9141f86)
Wed, 19 Jun 2013 11:27:09 GMT

Version 4.3.0b2 (0dd7f9fae13b)
Thu, 05 Sep 2013 08:25:02 GMT