Fix several user interaction bugs
Fix several user interaction bugs

* on hardy, entering invalid values caused apport "quit unexpectedly" dialogs
  to pop up, even though stepconf was alive and well
* upon returning to an Axis Configuration page with invalid values, the
  "forward" button was erroneously enabled

cnc-club/linuxcnc,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,jaguarcat79/ILC-with-LinuxCNC,unseenlaser/machinekit,bmwiedemann/linuxcnc-mirror,EqAfrica/machinekit,RunningLight/machinekit,Cid427/machinekit,cdsteinkuehler/MachineKit,ArcEye/machinekit-testing,mhaberler/machinekit,EqAfrica/machinekit,bobvanderlinden/machinekit,araisrobo/machinekit,RunningLight/machinekit,Cid427/machinekit,bmwiedemann/linuxcnc-mirror,araisrobo/machinekit,aschiffler/linuxcnc,EqAfrica/machinekit,strahlex/machinekit,RunningLight/machinekit,mhaberler/machinekit,jaguarcat79/ILC-with-LinuxCNC,ArcEye/MK-Qt5,RunningLight/machinekit,ikcalB/linuxcnc-mirror,EqAfrica/machinekit,cdsteinkuehler/linuxcnc,bobvanderlinden/machinekit,ArcEye/MK-Qt5,Cid427/machinekit,EqAfrica/machinekit,bmwiedemann/linuxcnc-mirror,bobvanderlinden/machinekit,aschiffler/linuxcnc,ikcalB/linuxcnc-mirror,narogon/linuxcnc,strahlex/machinekit,cdsteinkuehler/linuxcnc,yishinli/emc2,jaguarcat79/ILC-with-LinuxCNC,unseenlaser/machinekit,cnc-club/linuxcnc,unseenlaser/machinekit,kinsamanka/machinekit,yishinli/emc2,bobvanderlinden/machinekit,bmwiedemann/linuxcnc-mirror,cnc-club/linuxcnc,unseenlaser/linuxcnc,mhaberler/machinekit,kinsamanka/machinekit,ArcEye/machinekit-testing,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,cnc-club/linuxcnc,ArcEye/MK-Qt5,unseenlaser/linuxcnc,ArcEye/MK-Qt5,Cid427/machinekit,ianmcmahon/linuxcnc-mirror,unseenlaser/linuxcnc,ikcalB/linuxcnc-mirror,araisrobo/machinekit,Cid427/machinekit,cdsteinkuehler/MachineKit,narogon/linuxcnc,bmwiedemann/linuxcnc-mirror,kinsamanka/machinekit,cdsteinkuehler/MachineKit,ArcEye/machinekit-testing,ianmcmahon/linuxcnc-mirror,mhaberler/machinekit,ArcEye/machinekit-testing,araisrobo/machinekit,cdsteinkuehler/linuxcnc,ArcEye/machinekit-testing,ianmcmahon/linuxcnc-mirror,araisrobo/linuxcnc,kinsamanka/machinekit,Cid427/machinekit,araisrobo/machinekit,unseenlaser/machinekit,yishinli/emc2,strahlex/machinekit,cdsteinkuehler/MachineKit,cdsteinkuehler/linuxcnc,strahlex/machinekit,strahlex/machinekit,mhaberler/machinekit,mhaberler/machinekit,kinsamanka/machinekit,unseenlaser/machinekit,bobvanderlinden/machinekit,cdsteinkuehler/linuxcnc,ianmcmahon/linuxcnc-mirror,narogon/linuxcnc,EqAfrica/machinekit,RunningLight/machinekit,kinsamanka/machinekit,ikcalB/linuxcnc-mirror,RunningLight/machinekit,mhaberler/machinekit,Cid427/machinekit,cdsteinkuehler/MachineKit,ianmcmahon/linuxcnc-mirror,narogon/linuxcnc,unseenlaser/machinekit,bobvanderlinden/machinekit,strahlex/machinekit,ArcEye/MK-Qt5,unseenlaser/machinekit,narogon/linuxcnc,Cid427/machinekit,ianmcmahon/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ArcEye/MK-Qt5,EqAfrica/machinekit,strahlex/machinekit,cnc-club/linuxcnc,kinsamanka/machinekit,ArcEye/MK-Qt5,araisrobo/machinekit,araisrobo/linuxcnc,aschiffler/linuxcnc,jaguarcat79/ILC-with-LinuxCNC,araisrobo/linuxcnc,yishinli/emc2,bobvanderlinden/machinekit,cnc-club/linuxcnc,RunningLight/machinekit,unseenlaser/machinekit,unseenlaser/linuxcnc,araisrobo/linuxcnc,ArcEye/machinekit-testing,bobvanderlinden/machinekit,ArcEye/MK-Qt5,ianmcmahon/linuxcnc-mirror,cdsteinkuehler/MachineKit,aschiffler/linuxcnc,ArcEye/machinekit-testing,cnc-club/linuxcnc,EqAfrica/machinekit,kinsamanka/machinekit,ArcEye/machinekit-testing,aschiffler/linuxcnc,mhaberler/machinekit,unseenlaser/linuxcnc,RunningLight/machinekit,araisrobo/machinekit,araisrobo/machinekit,araisrobo/machinekit,araisrobo/linuxcnc,cdsteinkuehler/linuxcnc,jaguarcat79/ILC-with-LinuxCNC