missing 'using' directives for join_if and join_if_regex added

missing #include <boost/algorithm/string/join.hpp> added to string_algo.hpp


[SVN r34122]

libs/algorithm

@@ -1 +1 @@
-Subproject commit d9bc7e800bb761e20968023e773d5e9b97d5ac21
+Subproject commit 8af639b7cfa9caba8d9e0cfc553ac220911bb756