Fix test for socket.getfqdn() to also include the name returned by
socket.gethostname() in the check for a valid return.

Also clarified docs (official and docstring) that the value from gethostname()
is returned if gethostbyaddr() doesn't do the job.
diff --git a/Doc/lib/libsocket.tex b/Doc/lib/libsocket.tex
index db0b767..1f5bcaa 100644
--- a/Doc/lib/libsocket.tex
+++ b/Doc/lib/libsocket.tex
@@ -202,8 +202,8 @@
 host.  To find the fully qualified name, the hostname returned by
 \function{gethostbyaddr()} is checked, then aliases for the host, if
 available.  The first name which includes a period is selected.  In
-case no fully qualified domain name is available, the hostname is
-returned.
+case no fully qualified domain name is available, the hostname as
+returned by \function{gethostname()} is returned.
 \versionadded{2.0}
 \end{funcdesc}