Split b2 dependencies into public and private.

build.jam

@@ -9,7 +9,6 @@ constant boost_dependencies :
     /boost/assert//boost_assert
     /boost/concept_check//boost_concept_check
     /boost/config//boost_config
-    /boost/core//boost_core
     /boost/predef//boost_predef
     /boost/static_assert//boost_static_assert
     /boost/throw_exception//boost_throw_exception

build/Jamfile.v2

@@ -7,10 +7,15 @@ import modules ;
 import testing ;
 import errors ;
 
+constant boost_dependencies_private :
+    /boost/core//boost_core
+    ;
+
 project : requirements
    # default to all warnings on:
    <warnings>all
    : common-requirements <library>$(boost_dependencies)
+   : requirements <library>$(boost_dependencies_private)
    ;
 
 local disable-icu = [ MATCH (--disable-icu) : [ modules.peek : ARGV ] ] ;