Eeschema: SCH_SHEET_PATH refactor.

* Derive SCH_SHEET_PATH from std::vector< SCH_SHEET* > and remove unnecessary
  assignment operator and list management functions.
* Remove function BuildSheetPathInfoFromSheetPathValue() since it was
  effectively an assignment operation.
* Replace all calls to BuildSheetPathInfoFromSheetPathValue() with assignment
  operator.
* Replace list management functions with vector management functions.
* Fix a error message that wasn't translatable.

eeschema/plot_schematic_PS.cpp

@@ -4,7 +4,7 @@
 /*
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
- * Copyright (C) 1992-2010 KiCad Developers, see change_log.txt for contributors.
+ * Copyright (C) 1992-2016 KiCad Developers, see change_log.txt for contributors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -62,18 +62,11 @@ void DIALOG_PLOT_SCHEMATIC::createPSFile( bool aPlotAll, bool aPlotFrameRef )
             if( sheetpath == NULL )
                 break;
 
-            list.Clear();
-
-            if( list.BuildSheetPathInfoFromSheetPathValue( sheetpath->Path() ) )
-            {
-                m_parent->SetCurrentSheet( list );
-                m_parent->GetCurrentSheet().UpdateAllScreenReferences();
-                m_parent->SetSheetNumberAndCount();
-                screen = m_parent->GetCurrentSheet().LastScreen();
-            }
-            else // Should not happen
-                return;
-
+            list = *sheetpath;
+            m_parent->SetCurrentSheet( list );
+            m_parent->GetCurrentSheet().UpdateAllScreenReferences();
+            m_parent->SetSheetNumberAndCount();
+            screen = m_parent->GetCurrentSheet().LastScreen();
             sheetpath = SheetList.GetNext();
         }
 
@@ -125,7 +118,8 @@ void DIALOG_PLOT_SCHEMATIC::createPSFile( bool aPlotAll, bool aPlotFrameRef )
             else
             {
                 // Error
-                msg.Printf( _( "Unable to create file '%s'.\n" ), GetChars( plotFileName.GetFullPath() ) );
+                msg.Printf( _( "Unable to create file '%s'.\n" ),
+                            GetChars( plotFileName.GetFullPath() ) );
                 reporter.Report( msg, REPORTER::RPT_ERROR );
             }