Small fixes/improvements to printed trees

[jpco]

; es.old -c 'echo {~ x ()}'
{~ x }
; es.new -c 'echo {~ x ()}'
{~ x}

; es.old -c 'echo @ {}; echo @ * {}'
@ * {}
@ *{}
; es.new -c 'echo @ {}; echo @ * {}'
@ *{}
@ *{}

; es.old -c 'echo {$(a b)}'
{$((a b))}
; es.new -c 'echo {$(a b)}'
{$(a b)}

; es.old -c 'echo {$()}'
{$}
; es.new -c 'echo {$()}'
{$()}

I don't love all these choices personally (I'd rather {~ x ()} than {~ x} and @ * {} rather than @ *{}), but concision is pretty valuable when stuffing these strings into the environment, so I won't fight too hard to add more characters than strictly necessary (Adding parens to {$} is necessary because {$} isn't actually valid syntax).