Debugger: Improve adapter error handling

Correctly reset state on missing Symbian gdb.
Provide "settings" options.
Reviewed-by: hjk <qtc-committer@nokia.com>

src/plugins/debugger/gdb/plaingdbadapter.cpp

@@ -345,7 +345,7 @@ void PlainGdbAdapter::emitAdapterStartFailed(const QString &msg)
     bool blocked = m_stubProc.blockSignals(true);
     m_stubProc.stop();
     m_stubProc.blockSignals(blocked);
-    emit adapterStartFailed(msg);
+    emit adapterStartFailed(msg, QString());
 }
 
 } // namespace Internal