installer: Use named prompt to abort or break installer steps.

* gnu/installer/steps.scm (run-installer-steps): Set up
'installer-step prompt.
* gnu/installer/newt/ethernet.scm (run-ethernet-page)
* gnu/installer/newt/final.scm (run-config-display-page,
run-install-failed-page)
* gnu/installer/newt/keymap.scm (run-layout-page, run-variant-page)
* gnu/installer/newt/locale.scm (run-language-page,
run-territory-page, run-codeset-page, run-modifier-page,
run-locale-page)
* gnu/installer/newt/network.scm (run-technology-page,
wait-service-online)
* gnu/installer/newt/page.scm (run-listbox-selection-page,
run-checkbox-tree-page)
* gnu/installer/newt/partition.scm (button-exit-action)
* gnu/installer/newt/services.scm (run-desktop-environments-cbt-page,
run-networking-cbt-page, run-other-services-cbt-page,
run-network-management-page)
* gnu/installer/newt/timezone.scm (run-timezone-page)
* gnu/installer/newt/user.scm (run-user-page)
* gnu/installer/newt/welcome.scm (run-menu-page)
* gnu/installer/newt/wifi.scm (run-wifi-page): Use the 'installer-step
prompt to abort.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

gnu/installer/newt/services.scm

@@ -46,9 +46,7 @@ to choose from them later when you log in.")
      #:checkbox-tree-height 9
      #:exit-button-callback-procedure
      (lambda ()
-       (raise
-        (condition
-         (&installer-step-abort)))))))
+       (abort-to-prompt 'installer-step 'abort)))))
 
 (define (run-networking-cbt-page)
   "Run a page allowing the user to select networking services."
@@ -65,9 +63,7 @@ system.")
      #:checkbox-tree-height 5
      #:exit-button-callback-procedure
      (lambda ()
-       (raise
-        (condition
-         (&installer-step-abort)))))))
+       (abort-to-prompt 'installer-step 'abort)))))
 
 (define (run-printing-services-cbt-page)
   "Run a page allowing the user to select document services such as CUPS."
@@ -85,9 +81,7 @@ system.")
      #:checkbox-tree-height 9
      #:exit-button-callback-procedure
      (lambda ()
-       (raise
-        (condition
-         (&installer-step-abort)))))))
+       (abort-to-prompt 'installer-step 'abort)))))
 
 (define (run-console-services-cbt-page)
   "Run a page to select various system adminstration services for non-graphical
@@ -130,9 +124,7 @@ client may be enough for a server.")
      #:button-text (G_ "Exit")
      #:button-callback-procedure
      (lambda _
-       (raise
-        (condition
-         (&installer-step-abort)))))))
+       (abort-to-prompt 'installer-step 'abort)))))
 
 (define (run-services-page)
   (let ((desktop (run-desktop-environments-cbt-page)))