Add support for more recent versions of libicu

[lloydwatkin]

See http://icu-project.org/apiref/icu4c/

API changes are documented in there. It seems the most recent versions of ubuntu are using 53, we should attempt to support the newer versions.

[sonnyp]

Hey, one of our system guy is telling me this:

Yeah. I've built it OK on 14.04 VM with libicu-dev 52.
Ubuntu 12.04 we use in prod does have old libicu-dev 48.
Both build OK with node 0.12. I have no warnings I had with 0.10.

[lloydwatkin]

Yeah I've had no issues on ubuntu with multiple version of libicu too.

[lloydwatkin]

This issue arises because people were having issues at reporting it to be version issues, but I think that was not actually the issue.

[sonnyp]

I guess we can just ask them to use Node.js 0.12 then.