Fix compile error for Boost.Iostreams on clang.

The test still fails at runtime, although I don't think that's anything
to do with the newline filter. It seems to be caused by the combination
of Boost.Test and `<boost/iostreams/filter/test.hpp>`.

[SVN r61531]

libs/iostreams

@@ -1 +1 @@
-Subproject commit bb51391533a4eadb76382e67b4215e0fd0201d4e
+Subproject commit 75f6f6e80998bbb799cda90f47af3b48663c853f