const-ness of function bindings is not enforced consistently

[zingales]

in the repl if you try to instantiate a variable that is a function name, no error is thrown. however, the variable is not instantiated.

however, if you create a function and do the same thing, in a function declaration, the variable is instantiated. I feel that these two methods should have the same result, since one should be able to run through a function line by line in the repl.

[JeffBezanson]

dup of #222.