title: Accessing both branches of preprocessor conditions in Roslyn syntax trees
body: <p>Trying to parse C# code with Microsoft.CodeAnalysis.CSharp 1.0.0, I noticed that Roslyn's <code>SyntaxFactory.ParseSyntaxTree</code> accepts preprocessor symbols in <code>CSharpParseOptions</code>, and produces a syntax tree with an unparsed <code>DisabledTextTrivia</code> encompassing the inactive branch.</p>
  <p>My question is the following: is there a way to make Roslyn fully parse both branches? If not, why not exactly? I expected the preprocessor symbols to be provided to Roslyn at the compilation phase, rather than at the syntax parsing phase.</p>
  <p>A use case would be a refactoring tool that modifies code in disabled code branches (as ReSharper does).</p>