revert changeset 2056. pdb_io.cc is missing

modules/io/pymod/__init__.py

modules/io/pymod/export_pdb_io.cc

modules/io/pymod/wrap_io.cc

modules/io/src/io_manager.cc

modules/io/src/mol/CMakeLists.txt

modules/io/src/mol/dcd_io.cc

modules/io/src/mol/entity_io_crd_handler.cc

modules/io/src/mol/entity_io_mae_handler.cc

modules/io/src/mol/entity_io_mae_handler.hh

modules/io/src/mol/entity_io_pdb_handler.cc

modules/io/src/mol/pdb_io.hh

modules/io/src/mol/pdb_reader.cc

modules/io/src/mol/pdb_reader.hh

modules/io/src/mol/pdb_writer.cc

modules/io/src/mol/pdb_writer.hh

modules/mol/base/pymod/export_atom.cc

modules/mol/base/src/atom_base.cc

modules/mol/base/src/atom_base.hh

modules/mol/base/src/coord_frame.hh

modules/mol/base/src/coord_source.cc