Added missing includes for std::istream.

Thanks to Quentin Fiard for the report.

git-svn-id: http://jsoncpp.svn.sourceforge.net/svnroot/jsoncpp/trunk/jsoncpp/include@276 1f120ed1-78a5-a849-adca-83f0a9e25bb6
diff --git a/json/reader.h b/json/reader.h
index 189da57..3d8f628 100644
--- a/json/reader.h
+++ b/json/reader.h
@@ -11,6 +11,7 @@
 # include "value.h"
 #endif // if !defined(JSON_IS_AMALGAMATION)
 # include <deque>
+# include <iosfwd>
 # include <stack>
 # include <string>