Go bindings: translate_fdb_options.go should generate error predicates as functions

The error predicates get generated as constants by go, but I couldn't find a place where this was exposed. In any case, it would probably be better if those were made available as a series of methods on the Error class (à la FDBException.java).

Start by reading go bindings/translate_fdb_options.go and compare the generated error handling with FDBException.java. Trace how the Go Error type is exposed, then verify that the generated bindings provide callable error predicates corresponding to the Java methods.

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