Multiple API keys in aliased sites

Issue Summary

Hi, I'm using several alias for some webs, which already run in a multisite setup, and if I set a key for example.com a key error raises when you visit example.net.
It happens because google keys are tied to a second level domain and I didn't find any way to create a wildcard key, like in re-captcha.
So I made some changes on the module and now I can set a key for every alias, the only caveat is that you have to set up every key on admin/settings/simplemap for every alias, or run drush -l example.com variable-set simplemap_googleapikey_example_com THEGOOGLEAPIKEYFOREXAMPLEDOTCOM.
But I think this patch is a good start point, because this step is done only once time when a new alias is set.