extend API to add possibility for checkin handlers check if it is amending operation

platform/dvcs-impl/src/com/intellij/dvcs/DvcsCommitAdditionalComponent.java

@@ -179,4 +179,8 @@ public abstract class DvcsCommitAdditionalComponent implements RefreshableOnComp
 
   @Nullable
   protected abstract String getLastCommitMessage(@NotNull VirtualFile repo) throws VcsException;
+
+  public boolean isAmend() {
+    return myAmend.isSelected();
+  }
 }

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/ui/CommitChangeListDialog.java

@@ -175,6 +175,11 @@ public class CommitChangeListDialog extends DialogWrapper implements CheckinProj
       ProjectLevelVcsManager.getInstance(project).getAllActiveVcss());
   }
 
+  @NotNull
+  public List<RefreshableOnComponent> getAdditionalComponents() {
+    return Collections.unmodifiableList(myAdditionalComponents);
+  }
+
   public static void commitPaths(final Project project, Collection<FilePath> paths, final LocalChangeList initialSelection,
                                  @Nullable final CommitExecutor executor, final String comment) {
     final ChangeListManager manager = ChangeListManager.getInstance(project);