This module defines a "button" object for use with the TV window
interface. A TV_field (a "changeable" TV_button) inherits all of
the functionality of the TV_button class, with the additional
functionality of being able to change its appearance (text, or label)
by reading from the "TV" screen.
V00.00 Kevin McGuire October 25, 1991
Original - derived from tv_button.h.
V00.01 James Holt February 28, 1992
Add window id and pointer to pass user data.
V00.02 James Holt March 11, 1992
Remove brackets around label.
V00.03 Andrew Braun October 7, 1996
get_label description was mislabeled set_label.
Corrected argument to TV_create_label so window id is i2.