Added a bunch of "concept" index entries.

Use trailing "()" on function names in running text.
diff --git a/Doc/lib/libthread.tex b/Doc/lib/libthread.tex
index edf21f3..fcee360 100644
--- a/Doc/lib/libthread.tex
+++ b/Doc/lib/libthread.tex
@@ -7,10 +7,16 @@
 threads of control sharing their global data space.  For
 synchronization, simple locks (a.k.a.\ \dfn{mutexes} or \dfn{binary
 semaphores}) are provided.
+\index{light-weight processes}
+\index{processes, light-weight}
+\index{binary semaphores}
+\index{semaphores, binary}
 
 The module is optional.  It is supported on Windows NT and '95, SGI
 IRIX, Solaris 2.x, as well as on systems that have a POSIX thread
 (a.k.a. ``pthread'') implementation.
+\index{pthreads}
+\indexii{threads}{posix}
 
 It defines the following constant and functions:
 
@@ -87,8 +93,8 @@
 \item
 Threads interact strangely with interrupts: the
 \code{KeyboardInterrupt} exception will be received by an arbitrary
-thread.  (When the \code{signal} module is available, interrupts
-always go to the main thread.)
+thread.  (When the \code{signal}\refbimodindex{signal} module is
+available, interrupts always go to the main thread.)
 
 \item
 Calling \code{sys.exit()} or raising the \code{SystemExit} exception is
@@ -96,8 +102,8 @@
 
 \item
 Not all built-in functions that may block waiting for I/O allow other
-threads to run.  (The most popular ones (\code{sleep}, \code{read},
-\code{select}) work as expected.)
+threads to run.  (The most popular ones (\code{sleep()}, \code{read()},
+\code{select()}) work as expected.)
 
 \item
 It is not possible to interrupt the \code{acquire()} method on a lock
@@ -109,6 +115,7 @@
 threads survive.  On SGI IRIX using the native thread implementation,
 they survive.  On most other systems, they are killed without
 executing ``try-finally'' clauses or executing object destructors.
+\indexii{threads}{IRIX}
 
 \item
 When the main thread exits, it doesn't do any of its usual cleanup