GSocket: set protocol when using g_socket_new_from_fd()

Otherwise, attempting to create a GSocketConnection from the socket
will likely return the wrong type, since the protocol won't match any
of the registered subtypes.

Also add the start of a GSocket test program (from davidz).

https://bugzilla.gnome.org/show_bug.cgi?id=627171

gio/tests/Makefile.am

@@ -42,6 +42,7 @@ TEST_PROGS +=	 		\
 	gdbus-addresses		\
 	network-address		\
 	gdbus-message		\
+	socket			\
 	$(NULL)
 
 if OS_UNIX
@@ -196,6 +197,9 @@ srvtarget_LDADD		  = $(progs_ldadd)
 network_address_SOURCE	  = network-address.c
 network_address_LDADD	  = $(progs_ldadd)
 
+socket_SOURCE		  = socket.c
+socket_LDADD		  = $(progs_ldadd)
+
 contexts_SOURCES	  = contexts.c
 contexts_LDADD		  = $(progs_ldadd) \
 	$(top_builddir)/gthread/libgthread-2.0.la
@@ -392,7 +396,7 @@ EXTRA_DIST += \
 	appinfo-test-gnome.desktop	\
 	appinfo-test-notgnome.desktop	\
 	gdbus-testserver.py
- 
+
 MISC_STUFF = test.mo
 
 test.mo: de.po