stagedfunctions don't work with default arguments

[timholy]

Another not-urgent thing that needs fixing with stagedfunctions:

julia> stagedfunction myfunc(x, a = 5)
           @show x, a
           :(x + a)
       end
myfunc (generic function with 2 methods)

julia> myfunc(7)
(x,a) = (Type{Int64},Int64)
ERROR: `+` has no method matching +(::Type{Int64}, ::Int64)
 in anonymous at no file
 in myfunc at none:2

Presumably we should either disable default arguments, or (better) substitute in the type of the default rather than its value during instantiation.

[JeffBezanson]

I would say the fix is to make the one argument definition not staged.

[timholy]

Thanks, Jeff!