function names can start with [0-9_] while symbols not

[Bert Wesarg]

Hi,

there is a small inconsistency for the syntax of function names. A
function name can be [A-Za-z0-9_]+. But symbol names can only be
[A-Za-z$][A-Za-z0-9_]+, So its impossible to call a function defined
as '_test', or '0hello'.

I post a patch shortly, to support the symbol pattern for function
definitions too.

Bert