Eeschema: SCH_SHEET_LIST improvements.

* Derive SCH_SHEET_LIST from std::vector rather than using internal array
  management.  Change all internal code to use iterators or array operator
  in loops.
* Allow creation of empty SCH_SHEET_LIST for external population for plotting
  and printing.
* Clean up print an plot code to take advantage of new SCH_SHEET_LIST behavior.
* Make BuildSheetList() public so list can be populated after creation.
* Update all instances of SCH_SHEET_LIST with the appropriate SCH_SHEET
  object on initialization.
* Create const and non-const version of SCH_SHEET_PATH::GetSheet().

eeschema/plot_schematic_PS.cpp

@@ -39,10 +39,9 @@
 void DIALOG_PLOT_SCHEMATIC::createPSFile( bool aPlotAll, bool aPlotFrameRef )
 {
     SCH_SCREEN*     screen = m_parent->GetScreen();
-    SCH_SHEET_PATH* sheetpath;
-    SCH_SHEET_PATH  oldsheetpath = m_parent->GetCurrentSheet();     // sheetpath is saved here
-    PAGE_INFO       actualPage;                                     // page size selected in schematic
-    PAGE_INFO       plotPage;                                       // page size selected to plot
+    SCH_SHEET_PATH  oldsheetpath = m_parent->GetCurrentSheet();  // sheetpath is saved here
+    PAGE_INFO       actualPage;                                  // page size selected in schematic
+    PAGE_INFO       plotPage;                                    // page size selected to plot
 
     /* When printing all pages, the printed page is not the current page.
      * In complex hierarchies, we must update component references
@@ -50,26 +49,19 @@ void DIALOG_PLOT_SCHEMATIC::createPSFile( bool aPlotAll, bool aPlotFrameRef )
      *  because in complex hierarchies a SCH_SCREEN (a drawing )
      *  is shared between many sheets and component references depend on the actual sheet path used
      */
-    SCH_SHEET_LIST  SheetList( NULL );
+    SCH_SHEET_LIST  sheetList;
 
-    sheetpath = SheetList.GetFirst();
-    SCH_SHEET_PATH  list;
+    if( aPlotAll )
+        sheetList.BuildSheetList( g_RootSheet );
+    else
+        sheetList.push_back( m_parent->GetCurrentSheet() );
 
-    while( true )
+    for( unsigned i = 0; i < sheetList.size(); i++ )
     {
-        if( aPlotAll )
-        {
-            if( sheetpath == NULL )
-                break;
-
-            list = *sheetpath;
-            m_parent->SetCurrentSheet( list );
-            m_parent->GetCurrentSheet().UpdateAllScreenReferences();
-            m_parent->SetSheetNumberAndCount();
-            screen = m_parent->GetCurrentSheet().LastScreen();
-            sheetpath = SheetList.GetNext();
-        }
-
+        m_parent->SetCurrentSheet( sheetList[i] );
+        m_parent->GetCurrentSheet().UpdateAllScreenReferences();
+        m_parent->SetSheetNumberAndCount();
+        screen = m_parent->GetCurrentSheet().LastScreen();
         actualPage = screen->GetPageSettings();
 
         switch( m_pageSizeSelect )
@@ -129,9 +121,6 @@ void DIALOG_PLOT_SCHEMATIC::createPSFile( bool aPlotAll, bool aPlotFrameRef )
             msg.Printf( wxT( "PS Plotter exception: %s"), GetChars( e.errorText ) );
             reporter.Report( msg, REPORTER::RPT_ERROR );
         }
-
-        if( !aPlotAll )
-            break;
     }
 
     m_parent->SetCurrentSheet( oldsheetpath );