Fixing an API removal from Crittercism's SDK.

Not sure when this changed, but as of 4.1.1, `+setEmail:` doesn't exist. This should be backwards compatible with previous versions of Crittercism's SDK, but without knowing what happened when `+setEmail:` got called, I don't know if this is 100% accurate. Hopefully someone that's used `+setEmail:` can chime in?

This is related it issue #32.