control flow blocks with local assignments should not be rewritten as postfix expressions

[flavorjones]

Using syntax_tree v1.1.0. Rewriting the following code:

n = 1

if (b = n+1) > 1
  puts b
end

is rewritten as:

n = 1

puts b if (b = n + 1) > 1

which will cause an "undefined local variable or method" NameError exception to be raised.

[kddnewton]

Fixed by 802d647 and will be out in 1.1.1