"sg" should use arg types

[timholy]

It seems that even with enter_generated the arg value, rather than arg types, are being passed to the generator. Copied over from #157 (comment):

julia> @generated function f(x)
           :(return x)
       end
f (generic function with 1 method)

julia> callf() = f("Hello")
callf (generic function with 1 method)

julia> using JuliaInterpreter

julia> fr = JuliaInterpreter.enter_call(callf)
Frame for callf() in Main at REPL[2]:1
  1 1  1 ─ %1 = (f)("Hello")
  2 1  └──      return %1

julia> fr, pc = debug_command(fr, "s")
(Frame for f(x) in Main at REPL[1]:2
  1 2  1 ─     return x
x = "Hello"
caller: callf() in Main at REPL[2]:1, breakpoint(f(x) in Main at REPL[1]:2, %0))

julia> JuliaInterpreter.locals(fr)
2-element Array{JuliaInterpreter.Variable,1}:
 #self# = f 
 x = "Hello"

julia> fr = JuliaInterpreter.enter_call(callf)
Frame for callf() in Main at REPL[2]:1
  1 1  1 ─ %1 = (f)("Hello")
  2 1  └──      return %1

julia> fr, pc = debug_command(fr, "sg")
(Frame for f(x) in Main at REPL[1]:2
  1 2  CodeInfo(quote
x = "Hello"
caller: callf() in Main at REPL[2]:1, breakpoint(f(x) in Main at REPL[1]:2, %0))

julia> JuliaInterpreter.locals(fr)
2-element Array{JuliaInterpreter.Variable,1}:
 #self# = f 
 x = "Hello"

Shouldn't x = String? Note the CodeInfo(quote in the method body; the full expansion is

julia> fr.framecode.src
CodeInfo(quote
    return x
end)