Enable a smaller Intl (i18n / ICU) build

Implements joyent/node#7676 - see `README.md` for details.

Passes `make test` *as well as* current HEAD did (some network test failures?)

known TODOs:
- doc
  - [ ] Too much detail in the `README.md`. Move elsewhere/delete. 
- build
  - [ ] Windows build? Rewrite `icu-generic.sh` in python and/or use cygwin?
  - [ ] Switch to turn on and off "little by default"
  - [ ] Enable use of any ICU
- v8
  - [ ] need `InitializeICU` function https://code.google.com/p/v8/issues/detail?id=3344  ( workaround: could call the ICU functions directly from node..
- ICU
    - [ ] the "smaller ICU" changes could be pushed into a future ICU version.

NB: I have signed the CLA, you will find me under `srloomis` at US dot IBM dot COM