There were only two large classes of use for these variables:
1) Testing "funcdepth != 0" or "funcdepth > 0", which is equivalent to
checking "Curfn != nil".
2) In oldname, detecting whether a closure variable has been created
for the current function, which can be handled by instead testing
"n.Name.Curfn != Curfn".
Lastly, merge funcstart into funchdr, since it's only called once, and
it better matches up with funcbody now.