Function: ibut:key-to-label
ibut:key-to-label is a function alias for hbut:key-to-label, defined
in hbut.el.
Signature
(ibut:key-to-label LBL-KEY)
Documentation
Unnormalize LBL-KEY and return a label string for display.
If LBL-KEY is not a string or is just punctuation, return nil.