hush: deal with some easier TODOs

hush: deal with some easier TODOs

function                                             old     new   delta
is_well_formed_var_name                                -      87     +87
builtin_read                                          49      86     +37
die_if_script                                          -      31     +31
syntax_error_unterminated                              -      28     +28
syntax_error                                          26      51     +25
done_word                                            768     788     +20
syntax_error_at                                        -      12     +12
parse_stream_dquoted                                 320     328      +8
expand_variables                                    2064    2063      -1
run_list                                            1225    1220      -5
add_till_closing_paren                               308     303      -5
add_till_backquote                                   111     106      -5
handle_dollar                                        812     803      -9
parse_stream                                        2378    2356     -22
parse_redirect                                       408     372     -36
maybe_die                                             44       -     -44
is_assignment                                        215     134     -81
------------------------------------------------------------------------------
(add/remove: 4/1 grow/shrink: 4/8 up/down: 248/-208)           Total: 40 bytes