Fixed spelling error and clarified docs

docs/docs/howto_contribute.xml

@@ -419,7 +419,7 @@ for (int i = 0; i < my_std_vector.size(); ++i)
                   be able to easily find out what exception was thrown.  Additionally, exceptions typically contain a
                   message telling you all about the error.  Moreover, 
                   any debugger worth its
-                  salt will be able to show you a stack trace that let's you see exactly where the exception came from.
+                  salt will be able to show you a stack trace that lets you see exactly where the exception came from.
                    The exception <i>forces</i> you, the user, to 
                   be aware of this potential error and to add a catch block to deal with it. 
                   This is where the "hard to use wrong" comes from. 

docs/docs/intro.xml

@@ -120,8 +120,8 @@
                 broken rather than causing "undefined results")
 
                <br/><br/><u>ensures</u>:    This defines what the function does.  It is a list of conditions that will be 
-                true after the function finishes executing.  Note that if an exception is thrown or the function returns 
-                indicating an error occurred then nothing in the ensures clause is guaranteed to be true.
+                true after the function finishes executing.  Note that if an exception is thrown then nothing in the 
+                ensures clause is guaranteed to be true.
 
                <br/><br/><u>throws</u>:     This defines what exceptions may be thrown by this function.  It generally
                 tells you why the exception might be thrown.  It also tells you what the function does in this event: 
@@ -167,8 +167,8 @@
         - something &gt; 4     
     ensures
         - #some_other_function() == 9
-        - #funct() == something 
         - #something == something + 1
+        - returns something
 !*/</font>
 </code_box>