Split b2 dependencies into public and private.

build.jam

@@ -11,7 +11,6 @@ constant boost_dependencies :
     /boost/config//boost_config
     /boost/core//boost_core
     /boost/detail//boost_detail
-    /boost/function//boost_function
     /boost/integer//boost_integer
     /boost/io//boost_io
     /boost/iterator//boost_iterator

build/Jamfile.v2

@@ -10,11 +10,16 @@ require-b2 5.0.1 ;
 import-search /boost/config/checks ;
 import config : requires ;
 
+constant boost_dependencies_private :
+    /boost/function//boost_function
+    ;
+
 project
     : source-location ../src
     : common-requirements <library>$(boost_dependencies)
     : requirements
       <conditional>@include-spirit
+      <library>$(boost_dependencies_private)
     : usage-requirements
         <define>BOOST_SERIALIZATION_NO_LIB=1
 ;