Bug fix: Ensure to unescape special MSBuild characters.

I have a csproj file with an @ sign in it, as a dependency of the csproj file I'm building. This file is thus resolved as a reference by looking at the Include attribute which comes out as "%40...". So special MSBuild characters in that string are not unescaped. See http://msdn.microsoft.com/en-us/library/ms228186.aspx .