pass on error messages from salesforce

[simondawdry]

Using salesforceCreate() as a basic example you get the id of the newly created row back, however if it is unsuccessful you only get an empty string.

I believe there are error details from the salesforce api available which could be passed on through here -- would be great to see error details if say we were missing some required keys when attempting to create a record (i.e. if a formula has been applied to a particular field in an object requiring other keys to be set), or indeed if we have simply been rate limited or perhaps there's an invalid key in a query.