make ns-form-for-file available to leiningen, close #16

Needed for test subcommand:
https://github.com/technomancy/leiningen/commit/5cc3aa874bb7474ad835afae6676945695de1571#L0R113
Merge pull request #17 from cldwalker/make-ns-form-for-file-public

make ns-form-for-file available to leiningen, close #16