attempt more uniform handling of list concatenation in the parser * parse.h, oct-parse.yy (append_if_clause, append_switch_case, append_function_body, append_classdef_property, append_classdef_event, append_classdef_enum, append_classdef_superclass, append_classdef_attribute, append_classdef_properties_block, append_classdef_methods_block, append_classdef_events_block, append_classdef_enum_block, append_classdef_method, append_decl_init_list, append_argument_list): New base_parser methods. Use them to simplify actions in parser grammar. * pt-idx.h, pt-idx.cc (tree_index_expression::append): Return pointer to this. Change uses where needed.

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