Merge Boost.Build from trunk.

Note that since regression tests are using trunk Boost.Build,
this is already tested.


[SVN r57186]

tools/build

@@ -1 +1 @@
-Subproject commit 1ebf7d53867d0904fddd6839285dc7004a7d16b7
+Subproject commit afddf088b8a5f7ce21a3d69fd50fa96ee50d3965