Merge 75733 from the trunk.

[SVN r75758]

boostcpp.jam

@@ -80,7 +80,7 @@ if $(layout) = system && $(build-type) = complete
     ECHO "error: Cannot use --layout=system with --build-type complete." ;
     ECHO "error: Please used either --layout=versioned or --layout=tagged " ;
     ECHO "error: if you wish to build multiple variants." ;
-    if ! [ os.name ] = NT
+    if [ os.name ] != NT
     {        
         ECHO "error: Note that --layout=system is default on Unix starting with Boost 1.40." ;
     }