hush: make

hush: make
 a=55; echo $(($a + 1)) $((1 + $((2)) + `echo $a`))
 work as expected

function                                             old     new   delta
handle_dollar                                          -     667    +667
parse_stream_dquoted                                   -     316    +316
expand_variables                                    2124    2272    +148
is_assignment                                        134     215     +81
parse_stream                                        2038    1240    -798
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 2/1 up/down: 1212/-798)         Total: 414 bytes