[Bug #1209880] Describe only the True/False return values from lock.acquire()

Doc/lib/libthread.tex

@@ -81,11 +81,11 @@ Lock objects have the following methods:
 Without the optional argument, this method acquires the lock
 unconditionally, if necessary waiting until it is released by another
 thread (only one thread at a time can acquire a lock --- that's their
-reason for existence), and returns \code{None}.  If the integer
+reason for existence).  If the integer
 \var{waitflag} argument is present, the action depends on its
 value: if it is zero, the lock is only acquired if it can be acquired
 immediately without waiting, while if it is nonzero, the lock is
-acquired unconditionally as before.  If an argument is present, the
+acquired unconditionally as before.  The
 return value is \code{True} if the lock is acquired successfully,
 \code{False} if not.
 \end{methoddesc}

Doc/lib/libthreading.tex

@@ -167,8 +167,7 @@ All methods are executed atomically.
 Acquire a lock, blocking or non-blocking.
 
 When invoked without arguments, block until the lock is
-unlocked, then set it to locked, and return.  There is no
-return value in this case.
+unlocked, then set it to locked, and return true.  
 
 When invoked with the \var{blocking} argument set to true, do the
 same thing as when called without arguments, and return true.