clroni should have access to the error code enum on onidefs.h

[jonnew]

Currently, this enum is not reproduced in clroni

liboni/api/liboni/onidefs.h

Line 27 in e1b0916

enum {

with the idea being that the ONIException.cs class providing a higher-level representation of these errors, obviating low-level names of error codes. However, if we want to e.g. efficiently propagate or eat exceptions depending on their type, we end up manually reproducing the the error numbers in code that uses clroni, which is not good.