macro hygiene bug

[vtjnash]

this is a bit convoluted to come up with a good example, but macro hygiene is wrong for macros that return calls to macros:

# time: 2017-06-08 18:41:45 EDT
# mode: julia
        macro a()
          esc(:a)
        end
# time: 2017-06-08 18:41:58 EDT
# mode: julia
        macro b()
          :(@a)
        end
# time: 2017-06-08 18:42:16 EDT
# mode: julia
        function c()
          a = 1
          return @b
        end
# time: 2017-06-08 18:42:22 EDT
# mode: julia
        a = 2
        @test c() == 2

It seems like we're running hygiene over the AST before recursively expanding macros, whereas we should be doing it afterwards.

[JeffBezanson]

Maybe a good opportunity to revisit #10940.