Search for site-config.jam and user-config.jam not

only in BOOST_BUILD_PATH but also in HOME and
system locations. Document the search paths.


[SVN r16486]

tools/build

@@ -1 +1 @@
-Subproject commit cc3d8a96d2aaf86704d855ee5cac06c529a1ec6c
+Subproject commit 03fae257a80bfc94b6a17e2bde288baaaa82f439