[DP-66] TH-free API for working with Closures

[qnikst]

[Imported from JIRA. Reported by Tim Watson [Administrator] @hyperthunk) as DP-66 on 2013-02-11 22:56:25]
Integrate the changes described in https://groups.google.com/forum/?fromgroups=#!topic/cloud-haskell-developers/Xb39WZSCdTI