[MAJOR] implemented client-side support for PF_UNIX sockets

A new file, proto_uxst.c, implements support of PF_UNIX sockets
of type SOCK_STREAM. It relies on generic stream_sock_read/write
and uses its own accept primitive which also tries to be generic.

Right now it only implements an echo service in sight of a general
support for start dumping via unix socket. The echo code is more
of a proof of concept than useful code.
diff --git a/Makefile.osx b/Makefile.osx
index 5d6d875..a1a6c47 100644
--- a/Makefile.osx
+++ b/Makefile.osx
@@ -98,7 +98,7 @@
 OBJS = src/haproxy.o src/sessionhash.o src/base64.o src/protocols.o \
        src/uri_auth.o src/standard.o src/buffers.o src/log.o src/task.o \
        src/time.o src/fd.o src/regex.o src/cfgparse.o src/server.o \
-       src/checks.o src/queue.o src/client.o src/proxy.o \
+       src/checks.o src/queue.o src/client.o src/proxy.o src/proto_uxst.o \
        src/proto_http.o src/stream_sock.o src/appsession.o src/backend.o \
        src/session.o src/hdr_idx.o src/ev_select.o src/ev_poll.o src/acl.o \
        src/memory.o