Hashing test fails

[timholy]

Copied from #13 (comment), CC @macd

Ran the hashing module following instructions above (using today's master) most of the tests pass but saw the following:

mod = Main.JuliaTests
ex = quote
#= /home/macd/julia/test/hashing.jl:188 =#
let a = Expr(:block, Core.TypedSlot(1, Any)), b = Expr(:block, Core.TypedSlot(1, Any)), c = Expr(:block, Core.TypedSlot(3, Any))
#= /home/macd/julia/test/hashing.jl:191 =#
#= /home/macd/julia/test/hashing.jl:191 =# @test a == b && hash(a) == hash(b)
#= /home/macd/julia/test/hashing.jl:192 =#
#= /home/macd/julia/test/hashing.jl:192 =# @test a != c && hash(a) != hash(c)
#= /home/macd/julia/test/hashing.jl:193 =#
#= /home/macd/julia/test/hashing.jl:193 =# @test b != c && hash(b) != hash(c)
end
end
hashing: Error During Test at /home/macd/julia/test/hashing.jl:191
Test threw exception
Expression: a == b && hash(a) == hash(b)
syntax: Slot objects should not occur in an AST
hashing: Error During Test at /home/macd/julia/test/hashing.jl:192
Test threw exception
Expression: a != c && hash(a) != hash(c)
syntax: Slot objects should not occur in an AST
hashing: Error During Test at /home/macd/julia/test/hashing.jl:193
Test threw exception
Expression: b != c && hash(b) != hash(c)
syntax: Slot objects should not occur in an AST