Use real m-dashes instead of --

[SVN r77665]

v2/doc/src/reference.xml

@@ -411,7 +411,7 @@ path-constant DATA : data/a.txt ;
             feature, except that it takes effect only for linking. When you want
             to link all targets in a Jamfile to certain library, the
             <code>&lt;library&gt;</code> feature is preferred over
-            <code>&lt;source&gt;X</code> -- the latter will add the library to
+            <code>&lt;source&gt;X</code>&mdash;the latter will add the library to
             all targets, even those that have nothing to do with libraries.
           </simpara>
         </listitem>

v2/doc/src/tasks.xml

@@ -28,7 +28,7 @@ exe hello : hello.cpp some_library.lib /some_project//library
           : <threading>multi
           ;
 </programlisting>
-      This will create an executable file from the sources -- in this case, one
+      This will create an executable file from the sources&mdash;in this case, one
       C++ file, one library file present in the same directory, and another
       library that is created by Boost.Build. Generally, sources can include C
       and C++ files, object files and libraries. Boost.Build will automatically