RequestGroup::getNextCommand() was renamed to
createNextCommand().
Added its overloaded method.
* src/RequestGroup.h
(_numConcurrentCommand): New variable.
(setNumConcurrentCommand): New function.
* src/RequestGroup.cc
Abort download if same file is being downloaded concurrently.
* src/RequestGroup.h, src/RequestGroupMan.cc
(isSameFileBeingDownloaded): New function.
* src/HttpResponseCommand.cc (executeInternal)
* src/FtpNegotiateCommand.cc (recvSize)
* src/message.h (EX_DUPLICATE_FILE_DOWNLOAD): New definition.
* main.cc: Added help message for -i option.
Tatsuhiro Tsujikawa