parfor keyword and infrastructure, but handle parfor as normal for loop for now * octave.gperf (octave_kw_id): New keyword ids, parfor_kw and end_parfor_kw. (octave_kw): Add parfor and end_parfor to the struct. * lex.ll (is_keyword_token): Handle parfor and end_parfor. * token.h (token::parfor_end): New end_tok_type enum value. * oct-parse.yy (PARFOR): New token. (loop_command): Handle PARFOR statements. (make_for_command): New args tok_id and maxproc. Handle PARFOR loops. * pt-loop.h (tree_simple_for_command::parallel, tree_simple_for_command:maxproc): New data members. (tree_simple_for_command::tree_simple_for_command): New args parallel_arg and maxproc_arg. Initialize new data members. (tree_simple_for_command::parallel): New function. (tree_simple_for_command::maxproc_expr): New function. * pt-loop.cc (tree_simple_for_command::~tree_simple_for_command): Delete maxproc. (tree_simple_for_command::dup): Pass parallel and maxproc to constructor for duplicate object. * pt-pr-code.cc (tree_print_code::visit_simple_for_command): Handle parallel form. * pt-check.cc (tree_checker::visit_simple_for_command): Likewise. * pt-eval.cc (tree_evaluator::visit_simple_for_command): Note that this is where parallel loops need to be handled.