PySNMP: Protocol: API: Alpha: Get/Response PDU API methods

### Alpha API to Get/Response PDU objects

Alpha API to GetResponsePdu/ ResponsePdu objects inherits all Request PDU API methods and implements the following in addition:

apiAlphaGetErrorStatus()

  Returns a reference to ErrorStatus object.

apiAlphaSetErrorStatus(value)

  Stores value as Error Status at PDU where value is either a ErrorStatus object or a value suitable for ErrorStatus object initialization.

apiAlphaGetErrorIndex()

  Returns a reference to ErrorIndex object.

apiAlphaSetErrorIndex(value)

  Stores value as Error Index at PDU where value is either a ErrorIndex object or a value suitable for ErrorIndex object initialization.

apiAlphaGetEndOfMibIndices()

  Returns a list of VarBindList indices each of which indicate errornous VarBind position.

apiAlphaSetEndOfMibIndices(*indices)

  Indicate End-Of-MIB condition for VarBind's those position on VarBindList is indicated by the indices arguments.