Items are stored in the resource file by reference to the N item in the
validation string of the master icon.  On reading the templates file,
the N entry will be used to determine the items present, and to construct
a list of ItemRecs.  The N entries will be removed from the validation strings
and not put back till writing the file out again.

The "S" entry for indirected Sprite + Text icons is a special case.
It will be sucked out of the validation string before opening the editing
dbox, and displayed for editing in a special field.  Whether the
icon is Text, Sprite or T+S will be determined by whether these fields
contain anything or not when the user clicks OK.  The validation
string will then be updated to include the new sprite name.

Start edit:

IF_INDIR
        IF_TEXT:
                sprite null, text from [0]
        IF_SPRITE:
                text null, sprite from [0]
        IF_TEXT | IF_SPRITE
                text from [0], sprite from validation


End edit:
        both null:
                ?
        text ok, sprite null
                IF_TEXT, text in [0]
        text null, sprite ok
                IF_SPRITE, sprite in [0]
        both ok
                IF_TEXT | IF_SPRITE, text in [0], put sprite in valid string.
