Validation of IBAN (Internation Bank Account Number)

Please have a look at this. Although it works for me, there are a few things to think about:

(second try for pull request, previous one was mixed up with PR #628, so this time created new local branch, based before the other changes)

- IBAN will be introduced all over EU (and more) over the next years, maybe it should be in the main validate.js, and not in additional methods? At least it is a reason to think it over carefully: naming, location, maybe split per country.

- the code is quite long, maybe it can be shorter / more efficient? Especially the way the regexp for the country specific check can be build in other ways, or even be defined directly for every country (longer, but more clear: now a 'definition' string is parsed to build the regexp)

- There is a country-specific format check done now, just before the 'real' checksum check. This helps to block invalid IBANs (correct checksum, but incorrect country specific format) but will also block valid IBANS if a new country starts to use IBAN or if a country specific format will change in the future (I doubt the latter will ever happen, the first will though). So I think we should eigther provide 2 checks (iban and ibanwithoutcountrycheck) OR allow unknown countries, and just for those not check the format....

- At least in theory the check could be more specific, as within the 'local' account number there can be another checksum / limitations that are not checked now. I think this is not really needed though, as the checksum in the IBAN itself is quite strong and countries may stop using their local restrictions anyway to just rely in IBAN in the future.