Fixed documentation errors (typos and formatting) in chapter

chapter "Advanced FLTK" (Multithreading) and added a short
explanation to sending and retrieving messages.


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@8047 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

documentation/src/advanced.dox

@@ -7,7 +7,7 @@ that will help you to get the most out of FLTK.
 
 \section advanced_multithreading Multithreading
 
-FLTK supports multithreaded application using a locking mechanism
+FLTK supports multithreaded applications using a locking mechanism
 based on "pthreads". We do not provide a threading interface as part of
 the library.  However a simple example how threads can be implemented
 for all supported platforms can be found in \p test/threads.h
@@ -30,7 +30,7 @@ locked:
     int main() {
       Fl::lock();
       /* run thread */
-      while (Fl::wait() > 0) {
+      while (Fl::wait() > 0) {
         if (Fl::thread_message()) {
           /* process your data */
         }
@@ -56,6 +56,9 @@ using Fl::awake(void* message):
     Fl::awake(msg);  // send "msg" to main thread
 \endcode
 
+A message can be anything you like. The main thread can retrieve
+the message by calling Fl::thread_message(). See example above.
+
 You can also tell the main thread to call a function for you
 as soon as possible by using
 Fl::awake(Fl_Awake_Handler cb, void* userdata):
@@ -72,9 +75,9 @@ Fl::awake(Fl_Awake_Handler cb, void* userdata):
 
 
 FLTK supports multiple platforms, some of which allow only the
-the main thread to handle system events and
-open or close windows. The safe thing to do is to adhere to the 
-following rules for threads on all operating systems:
+main thread to handle system events and open or close windows.
+The safe thing to do is to adhere to the following rules for
+threads on all operating systems:
 
 
 \li Don't \p show() or \p hide() anything that contains