fixup_after_fork (bool, HANDLE).
* fhandler_socket.cc (fhandler_socket::fixup_after_fork): Move
functionality to new private method. Add closing parent socket
if not called from dup(). Create method new calling private method
with appropriate parameter.
(fhandler_socket::fixup_after_exec): Call private method
fixup_after_fork with appropriate parameter.
(fhandler_socket::dup): Ditto.