handle absolute path in /// references

Author: mhegazy

src/compiler/parser.ts

@@ -4019,7 +4019,8 @@ module ts {
 
         function processReferencedFiles(file: SourceFile, basePath: string) {
             forEach(file.referencedFiles, ref => {
-                processSourceFile(normalizePath(combinePaths(basePath, ref.filename)), /* isDefaultLib */ false, file, ref.pos, ref.end);
+                var referencedFilename = isRootedDiskPath(ref.filename) ? ref.filename : combinePaths(basePath, ref.filename);
+                processSourceFile(normalizePath(referencedFilename), /* isDefaultLib */ false, file, ref.pos, ref.end);
             });
         }