Move the documentation for the mutex module to be with the threading

and queue-management modules, since that is where the general context
for use in most cases.

Doc/lib/lib.tex

@@ -147,7 +147,6 @@ and how to embed it in other applications.
 \input{libshutil}
 \input{liblocale}
 \input{libgettext}
-\input{libmutex}
 
 \input{libsomeos}		% Optional Operating System Services
 \input{libsignal}
@@ -155,6 +154,7 @@ and how to embed it in other applications.
 \input{libselect}
 \input{libthread}
 \input{libthreading}
+\input{libmutex}
 \input{libqueue}
 \input{libmmap}
 \input{libanydbm}