0.5.0-rc2+0 segfault

[denizyuret]

Two issues with the following code:

1. There is a warning I don't get in 0.4: WARNING: Method definition #1(Any) in module Main at foo.jl:5 overwritten at foo.jl:5.
2. The code segfaults.

foo(a,x...)=(randn(),)

for (f,g) in ((:asin,:sin), (:acos,:cos))
    gx = eval(g)
    foo(::Type{Val{f}},x...)=map(x->2gx(x),foo(Val{b},x...))
end

foo(Val{:asin},3)

[ViralBShah]

Verified - crashes on master.

[JeffBezanson]

Why is this release-blocking ahead of, say, #17003 #17288 #18069?