Make sure that the crc for zlib is reset when we reuse a filter. This should fix the gzip errors that I'm seeing in the trunk tests.

[SVN r62984]

libs/iostreams

@@ -1 +1 @@
-Subproject commit af4492179234b3b9441796230108b4def2d91417
+Subproject commit b4640aff4038e54a59d79ec7cb2fbb7af651ce64