Fix #846. Allow negative options such as "nolisten=1" in bitcoin.conf as well as on the command line. #847

I copied this whole block out of ParseParameters() and changed the variable names.

Perhaps it's better to move this code into a new function and call it from both places.

Or we could just process all the "-no" parameters at once, after bitcoin.conf has been processed.

The "--" -> "-" processing needs to stay where it is, however, so that --datadir= can be used to locate bitcoin.conf.

I think a separate method called from ParseParameters and ReadConfigFile is the better way to go.