Avoid non-inline non-template functions in headers.

This fixes #2406. gzip.hpp had a few functions
that are not templates or inline, which caused link errors.
Since the functions are fairly big, this patch moves
them into a cpp file.


[SVN r53427]

libs/iostreams

@@ -1 +1 @@
-Subproject commit 34b1cf248773aa9bc1b510b19441d70e6453bcd1
+Subproject commit 4aff4b1ee9ac23f6e53513429d4b8579a21dd073