Disable the "OK" and "Apply" buttons before calling the apply function.

[David Hampton]

Log Message:
-----------
Disable the "OK" and "Apply" buttons before calling the apply
function.  Makes the UI appear more responsive and prevents a crash if
the user clicks Apply then OK quickly. (#319546) Patch from Arnout
'raboof' Engelen <gnomebugzilla at bzzt.net>.

Tags:
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gnucash-gnome2-dev

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/gnome-utils:
        dialog-options.c