ENH: finer granularity for handling functionObject failure (#1779)

• additional "errors" entry with enumerated values (default|warn|ignore|strict) for defining warning or error at construct or runtime stage

• default : construct = warn, runtime = fatal

• warn : construct = warn, runtime = warn

• ignore : construct = silent, runtime = silent

• strict : construct = fatal, runtime = fatal

The errors control can be added at the top-level and/or for individual function objects.