Changed semantics of Open and Import.

Their names now reflect the action taken: Open opens a Merkaartor document,
Import imports files into the current document.

This is mostly to eliminate the magical code that guesses what should be done
based on files, and is different in import and open actions.

src/MainWindow.cpp

@@ -132,6 +132,7 @@ class MainWindowPrivate
             title = QString("%1 v%2").arg(STRINGIFY(PRODUCT)).arg(STRINGIFY(REVISION));
         }
 
+        QString FILTER_OPEN_NATIVE;
         QString FILTER_OPEN_SUPPORTED;
         QString FILTER_IMPORT_SUPPORTED;
         int lastPrefTabIndex;
@@ -203,6 +204,8 @@ MainWindow::MainWindow(QWidget *parent)
     supported_import_formats_desc += tr("Protobuf Binary Format (*.pbf)\n");
 #endif
 
+    p->FILTER_OPEN_NATIVE = tr("Merkaartor document (*.mdc)\n");
+
     p->FILTER_OPEN_SUPPORTED = QString(tr("Supported formats") + " (*.mdc %1)\n").arg(supported_import_formats);
     p->FILTER_OPEN_SUPPORTED += tr("Merkaartor document (*.mdc)\n") + supported_import_formats_desc;
     p->FILTER_OPEN_SUPPORTED += tr("All Files (*)");
@@ -497,14 +500,16 @@ void MainWindow::handleMessage(const QString &msg)
                 loadUrl(u);
                 continue;
             }
-            fileNames.append(args[i]);
+            if (args[i].endsWith(".mdc", Qt::CaseInsensitive))
+                loadDocument(args[i]);
+            else
+                fileNames.append(args[i]);
         }
     }
 
-    if (fileNames.isEmpty())
-        QDir::setCurrent(M_PREFS->getworkingdir());
-    else
-        loadFiles(fileNames);
+    if (fileNames.size() > 0) {
+        importFiles(theDocument, fileNames, NULL);
+    }
 }
 
 MainWindow::~MainWindow(void)
@@ -2018,12 +2023,10 @@ void MainWindow::on_fileOpenAction_triggered()
     if (hasUnsavedChanges() && !mayDiscardUnsavedChanges(this))
         return;
 
-    QStringList fileNames = QFileDialog::getOpenFileNames(
-                    this,
-                    tr("Open files"),
-                    QString(), p->FILTER_OPEN_SUPPORTED);
+    QString fileName = QFileDialog::getOpenFileName(this, tr("Open file"), QString(), p->FILTER_OPEN_NATIVE );
 
-    loadFiles(fileNames);
+    if (!fileName.isNull())
+        loadDocument(fileName);
 }
 
 void MainWindow::on_fileUploadAction_triggered()
@@ -3876,8 +3879,8 @@ void MainWindow::recentOpenTriggered(QAction* anAction)
     if (hasUnsavedChanges() && !mayDiscardUnsavedChanges(this))
         return;
 
-    QStringList fileNames(anAction->text());
-    loadFiles(fileNames);
+    QString fileName(anAction->text());
+    loadDocument(fileName);
 }
 
 void MainWindow::recentImportTriggered(QAction* anAction)