Make config module availabe to subprojects

This makes it possible to `import config` instead of using a relative
path requiring package managers to patch the files.

Jamroot

@@ -294,6 +294,9 @@ if [ path.exists $(BOOST_ROOT)/libs/wave/tool/build ]
     use-project /boost/libs/wave/tool : libs/wave/tool/build ;
 }
 
+# Allow subprojects to simply `import config : requires ;` to get access to the requires rule
+modules.poke : BOOST_BUILD_PATH : $(BOOST_ROOT)/libs/config/checks [ modules.peek : BOOST_BUILD_PATH ] ;
+
 # Make the boost-install rule visible in subprojects
 
 # This rule should be called from libraries' Jamfiles and will create two