Make the schematic I/O plugin the only option.

Add SCH_PLUGIN object to PART_LIB object.

Convert all PART_LIB I/O to use SCH_PLUGIN.

Remove library caching from PART_LIB and use caching provided by SCH_PLUGIN.

Add support to use PROPERTIES for buffering and document file write control
instead of adding code the SCH_PLUGIN object in the SCH_LEGACY_PLUGIN that
will not be required when the new file formats are implemented.

Add buffering to SCH_LEGACY_PLUGIN to prevent cache from writing file on
every change to library.  This is to prevent the cache library from being
written every time a new symbol is added.

Add option to not save library document file when saving library.  This is
primarily used by the cache library write code.

Move symbol library write code out of LIB_PART and into SCH_LEGACY_PLUGIN.

Add exception handling where LIB_PART caught the exception and returned
an error status.

Remove KICAD_SCH_IO_MANAGER build option as it is no longer optional.

eeschema/sch_plugin.cpp

@@ -2,7 +2,7 @@
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
  * Copyright (C) 2016 CERN
- * Copyright (C) 2016 KiCad Developers, see change_log.txt for contributors.
+ * Copyright (C) 2016-2017 KiCad Developers, see change_log.txt for contributors.
  *
  * @author Wayne Stambaugh <[email protected]>
  *
@@ -41,6 +41,20 @@ static void not_implemented( SCH_PLUGIN* aPlugin, const char* aCaller )
 }
 
 
+static void not_implemented( const SCH_PLUGIN* aPlugin, const char* aCaller )
+{
+    THROW_IO_ERROR( wxString::Format( FMT_UNIMPLEMENTED,
+                                      aPlugin->GetName().GetData(),
+                                      wxString::FromUTF8( aCaller ).GetData() ) );
+}
+
+
+void SCH_PLUGIN::SaveLibrary( const wxString& aFileName, const PROPERTIES* aProperties )
+{
+    not_implemented( this, __FUNCTION__ );
+}
+
+
 SCH_SHEET* SCH_PLUGIN::Load( const wxString& aFileName, KIWAY* aKiway, SCH_SHEET* aAppendToMe,
                              const PROPERTIES* aProperties )
 {
@@ -57,16 +71,18 @@ void SCH_PLUGIN::Save( const wxString& aFileName, SCH_SCREEN* aSchematic, KIWAY*
 }
 
 
-void SCH_PLUGIN::EnumerateSymbolLib( wxArrayString&    aAliasNameList,
-                                     const wxString&   aLibraryPath,
-                                     const PROPERTIES* aProperties )
+size_t SCH_PLUGIN::GetSymbolLibCount( const wxString&   aLibraryPath,
+                                      const PROPERTIES* aProperties )
 {
     // not pure virtual so that plugins only have to implement subset of the SCH_PLUGIN interface.
     not_implemented( this, __FUNCTION__ );
+    return 0;
 }
 
 
-void SCH_PLUGIN::TransferCache( PART_LIB& aTarget )
+void SCH_PLUGIN::EnumerateSymbolLib( wxArrayString&    aAliasNameList,
+                                     const wxString&   aLibraryPath,
+                                     const PROPERTIES* aProperties )
 {
     // not pure virtual so that plugins only have to implement subset of the SCH_PLUGIN interface.
     not_implemented( this, __FUNCTION__ );