* cygwin.din (getpeereid): Export.
* fhandler.h (class fhandler_socket): Add pipe and id members to
exchange eid credentials for AF_LOCAL sockets.
(eid_pipe_name): Declare new method.
(getpeereid): Ditto.
* fhandler_socket.cc (fhandler_socket::eid_pipe_name): New method.
(fhandler_socket::fhandler_socket): Initialize sec_pipe.
(fhandler_socket::connect): Exchange eid credentials with accepting
socket process.
(fhandler_socket::listen): Prepare eid credential transaction.
(fhandler_socket::accept): Exchange eid credentials with connecting
socket process.
(fhandler_socket::close): Close eid credentials pipe if open.
(fhandler_socket::getpeereid): New method.
* net.cc (cygwin_getsockopt): Add SO_PEERCRED handling.
(getpeereid): New function.
* include/asm/socket.h (SO_PEERCRED): Define.
* include/cygwin/socket.h (struct ucred): Define new type.
* include/cygwin/version.h: Bump API minor version.
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