* lang/qt/src/protocol.h (class Protocol): Add member function
secretSubkeyExportJob.
* lang/qt/src/protocol_p.h (Protocol::secretSubkeyExportJob): Implement.
* lang/qt/tests/run-exportjob.cpp (showUsageAndExitWithCode): Print
new option.
(createExportJob): Create secret subkey export job if requested.
(main): New option --secret-subkey.