POSIX allows successful system calls to modify errno, so always clear the

error_code if the result indicates success. Fixes #2953.


[SVN r52465]

libs/asio

@@ -1 +1 @@
-Subproject commit b79f9a65cd764141c34ede2f45357234f4ea11f6
+Subproject commit 1f9ec4a8da8df922455924a26c6af970c46bce9a