* pym.el (defun-maybe): Use `defalias' instead of `defun';

* pym.el (defun-maybe): Use `defalias' instead of `defun';
 don't handle `current-load-list';
 always return a function symbol.
(defmacro-maybe): Set a symbol to a macro definition itself;
 don't handle `current-load-list';
 always return a macro symbol.
(defsubst-maybe): Set a symbol to a function definition itself;
 don't handle `current-load-list';
 always return a function symbol.
(defalias-maybe): Always return a new definition.
(defvar-maybe): Always return a variable symbol.
(defconst-maybe): Ditto.
(defun-maybe-cond): Use `defalias' instead of `defun';
 don't handle `current-load-list';
 always return a function symbol.
(defmacro-maybe-cond): Set a symbol to a macro definition itself;
 don't handle `current-load-list';
 always return a macro symbol.
(defsubst-maybe-cond): Set a symbol to a function definition itself;
 don't handle `current-load-list';
 always return a function symbol.
(defun-when-void): Always return a function symbol.
(defmacro-when-void): New macro.
(defsubst-when-void): New macro.
(defalias-when-void): New macro.
(defvar-when-void): New macro.
(defconst-maybe): New macro.