export functions from parse.y

[Muthiah Annamalai]

Hello JWE,

I request to export the functions

 is_function_file( )

as it helps in external tools, and possibly
in making the evaluating AST walker.

Also I would like a handle to the parsed function
after yyparse(), stored in octave_function* curr_fcn_ptr.
This is only accessible within parse.y, and Im not
aware of another way of accessing this other than
load_fcn_from_file(). This becomes a problem to me, when
theres a script file with a function definition inside it.
I cant seem to extract that out.

If you agree I can make the patches to export the symbols.

Thanks,
Muthu