Import: split process_imported_dives() function

Split the process_imported_dives() function in two:
1) process_imported_dives() processes the dives and generates
   a list of dives and trips to be added and removed.
2) add_imported_dives() calls process_imported_dives() and
   does the actual removal / addition of dives and trips.

The goal is to split preparation and actual work, to
make dive import undo-able.

The code adds extra checks to never merge into the same
dive twice, as this would lead to a double-free() bug.
This should in principle never happen, as dives that
compare equal according to is_same_dive() are merged
in the imported-dives list, but perhaps in some pathologival
corner-cases is_same_dive() turns out to be non-transitive.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

desktop-widgets/divelogimportdialog.cpp

@@ -1011,7 +1011,7 @@ void DiveLogImportDialog::on_buttonBox_accepted()
 		}
 	}
 
-	process_imported_dives(&table, &trips, false, false, true);
+	add_imported_dives(&table, &trips, false, false, true);
 	Command::clear();
 	MainWindow::instance()->refreshDisplay();
 }

desktop-widgets/downloadfromdivecomputer.cpp

@@ -525,9 +525,9 @@ void DownloadFromDCWidget::on_ok_clicked()
 		// remember the last downloaded dive (on most dive computers this will be the chronologically
 		// first new dive) and select it again after processing all the dives
 		int uniqId = table->dives[table->nr - 1]->id;
-		process_imported_dives(table, trips, preferDownloaded(), true, false);
+		add_imported_dives(table, trips, preferDownloaded(), true, false);
 		Command::clear();
-		// after process_imported_dives does any merging or resorting needed, we need
+		// after add_imported_dives does any merging or resorting needed, we need
 		// to recreate the model for the dive list so we can select the newest dive
 		MainWindow::instance()->recreateDiveList();
 		int idx = get_idx_by_uniq_id(uniqId);

desktop-widgets/mainwindow.cpp

@@ -1714,7 +1714,7 @@ void MainWindow::importFiles(const QStringList fileNames)
 		fileNamePtr = QFile::encodeName(fileNames.at(i));
 		parse_file(fileNamePtr.data(), &table, &trips);
 	}
-	process_imported_dives(&table, &trips, false, false, true);
+	add_imported_dives(&table, &trips, false, false, true);
 	Command::clear();
 	refreshDisplay();
 }

desktop-widgets/subsurfacewebservices.cpp

@@ -771,7 +771,7 @@ void DivelogsDeWebServices::buttonClicked(QAbstractButton *button)
 		struct dive_table table = { 0 };
 		struct trip_table trips = { 0 };
 		parse_file(QFile::encodeName(zipFile.fileName()), &table, &trips);
-		process_imported_dives(&table, &trips, false, false, true);
+		add_imported_dives(&table, &trips, false, false, true);
 		MainWindow::instance()->refreshDisplay();
 
 		/* store last entered user/pass in config */