Adjust errorcode in background worker code

Hi,

How about the attached that adjusts errorcode for the error related to
checking the flag bgw_flags in BackgroundWorkerInitializeConnection*()
functions so that it matches the treatment in SanityCheckBackgroundWorker()?

s/ERRCODE_PROGRAM_LIMIT_EXCEEDED/ERRCODE_INVALID_PARAMETER_VALUE/g

There is already a "/* XXX is this the right errcode? */" there.

Thanks,
Amit