XPdecode()
  Decode a string coded by XPencode()
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   Function:   XPdecode()

               See XPencode() for full details.
               In fact XPencode() is a symmetric function, meaning that
               Encoding a string with the same key twice returns the
               original string. a XPdecode() function, that thus is the
               same as XPencode(), has been added however, to make the
               programming clearer.

   Syntax:     XPdecode(<cCodedStr>,<cKey>) --> cStr

   Arguments:  <cCodedStr> is the string to decode. <cKey> is the keyword
               that was used by encode().

   Returns:    The string, normal again.

   Usage:      if x != XPdecode(XPencode(x,'xxx'),'xxx')
                    MouseAlert("We've got a;SERIOUS;problem here!")
               end