schematic: Fix define-action syntax to make it work with guile-2.2.

When compiled with guile-2.2, make-action() always returned the
same thunk (action()) which made define-action not working since
it redefined make-action() each time it was called by setting new
properties for the same thunk, thus using the last defined
action() for each and every menu item. This didn't affect
guile-2.0 due to, probably, more loose code compilation. The issue
has been fixed by moving thunk creation to define-action syntax
which allows creation of new procedures each time it is evaluated.

schematic/scheme/gschem/action.scm

@@ -98,16 +98,21 @@
   (false-if-exception
    (eq? %cookie (procedure-property proc 'gschem-cookie))))
 
+;;; define-action syntax defines a procedure being a result of
+;;; calling eval-action! on a dummy thunk with properties returned
+;;; by make-action. Those predefined properties include a new
+;;; thunk defined by FORMS, which will be the core of the result.
+;;; This allows you to invoke an action just by calling it like a
+;;; normal function.
 (define-syntax define-action
   (syntax-rules ()
     ((_ (name . args) . forms)
-     (define name (make-action (lambda () . forms) . args)))))
+     (define name
+       (lambda ()
+         (eval-action! (make-action (lambda () . forms) . args)))))))
 
 (define-public (make-action thunk . props)
-  ;; The action is a magical procedure that does nothing but call
-  ;; eval-action! *on itself*.  This allows you to invoke an action
-  ;; just by calling it like a normal function.
-  (letrec ((action (lambda () (eval-action! action))))
+  (let ((action (lambda () "Dummy action.")))
 
     ;; The action data is stored in procedure properties -- most
     ;; importantly, the actual thunk that the action wraps
@@ -126,9 +131,8 @@
                                  (keyword->symbol (list-ref lst 0))
                                  (list-ref lst 1))
            (loop (list-tail lst 2))))
-
-
 
+    ;; Return dummy thunk with properties.
     action))
 
 (define (action-thunk action)