Fix Issue 57: we cannot simply add offsets to a void *.

* outgoing.c:
  (socket_writev): cast iov_base properly, in order to increment it

Patch by: dongsheng song


git-svn-id: https://svn.apache.org/repos/asf/serf/tags/0.4.0@1698894 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/outgoing.c b/outgoing.c
index b4b3a50..11d58aa 100644
--- a/outgoing.c
+++ b/outgoing.c
@@ -470,7 +470,7 @@
                             sizeof(struct iovec) * (conn->vec_len - i));
                     conn->vec_len -= i;
                 }
-                conn->vec[0].iov_base += conn->vec[0].iov_len - (len - written);
+                ((char *) conn->vec[0].iov_base) += conn->vec[0].iov_len - (len - written);
                 conn->vec[0].iov_len = len - written;
                 break;
             }