Add filesystem library

[SVN r17949]

Jamfile

@@ -2,6 +2,7 @@ project-root ;
 
 # please order by name to ease maintenance
 subinclude libs/date_time/build ;
+subinclude libs/filesystem/build ;
 subinclude libs/python/build ;
 subinclude libs/regex/build ;
 subinclude libs/signals/build ;