Fixed browsing files history.

This is a regression since 2fed338.

We can't just clear current file name, because it's useful in some cases. For example if you browse commits for particular file that was selected in the left panel.

As far as I understand the goal is to open "Log" tab when different commit is pressed and open "Diff" tab when different filename is selected. This can be achieved by checking if sha has been changed.

Fixes #11

src/listview.cpp

@@ -250,7 +250,6 @@ void ListView::currentChanged(const QModelIndex& index, const QModelIndex&) {
 	SCRef selRev = sha(index.row());
 	if (st->sha() != selRev) { // to avoid looping
 		st->setSha(selRev);
-		st->setFileName("");
 		st->setSelectItem(true);
 		UPDATE_DOMAIN(d);
 	}

src/revsview.cpp

@@ -280,7 +280,8 @@ bool RevsView::doUpdate(bool force) {
 		}
 		if (st.isChanged() || force) {
 			// activate log or diff tab depending on file selection
-			tab()->tabLogDiff->setCurrentIndex(st.fileName().isEmpty() ? 0 : 1);
+			bool sha_changed = st.sha(true) != st.sha(false);
+			tab()->tabLogDiff->setCurrentIndex(sha_changed ? 0 : 1);
 			tab()->textEditDiff->centerOnFileHeader(st);
 		}