This will only work if the first non-comment form of the 'helper' or
'extension' source file is an (in-ns) form. It will not look for any
subsequent in-ns forms in the file. This is the same idiomatic usage of
load/in-ns that is found in clojure/core.
-- newer-namespace-decls returns a list of ns-decls (as before) but also
a set of namespace names (symbols) that have been affected.
-- avoid calling .fileModifed twice
-- replace contains? (as in
-- use tools.namespace 0.2.2 (similarly to
-- use clojure 1.3.0 (required by tools.namespace)