Improve printing of macroexpand(:(@inbounds foo))

More along the lines of #7775. This one is a little scarier, but it seems to work. I'm submitting now, and I'll let others decide whether this should wait.

Before:
```julia
julia> ex = quote
       for i = 1:length(a)
           @inbounds s += a
       end
       end
quote  # none, line 2:
    for i = 1:length(a) # line 3:
        @inbounds s += a
    end
end

julia> macroexpand(ex)
quote  # none, line 2:
    for i = 1:length(a) # line 3:
        begin 
            $(Expr(:boundscheck, false))
            begin 
                s += a
                $(Expr(:boundscheck, :(Base.pop)))
            end
        end
    end
end
```
Now:
```julia
julia> macroexpand(ex)
quote  # none, line 2:
    for i = 1:length(a) # line 3:
        @inbounds begin 
            s += a
        end
    end
end
```