add another POSIX semaphore example and add reference

Author: vladak

synchro.tex

@@ -666,6 +666,7 @@
 \item Example on POSIX semaphores (it is a fixed version of the previous example
 \example{race/race.c} from page \pageref{RACE_C}):
 \example{race/posix-sem-fixed-race.c}.
+\item Another example: \example{semaphores/talking-heads.c}
 \end{itemize}
 
 %%%%%

threads.tex

@@ -1424,8 +1424,8 @@
 
 \begin{itemize}
 \item Semaphores created using this API do not have a name (as opposed to
-those created via the \texttt{sem\_open} function), hence they are called
-unnamed.
+those created via the \texttt{sem\_open} function,
+see page \pageref{NAMED_SEMAPHORES}), hence they are called unnamed.
 \item The semaphore functions adhere to the classical UNIX semantics --
 they return -1 on error and set \texttt{errno}.
 \item Example: \example{semaphores/sem.c}