PROGRAM
	detab convert tabs to blanks
USAGE
	detab
DESCRIPTION
	detab copies its input to its output, expanding horizontal tabs to blanks
	along the way, so that the output is visually the same as the input, but
	contains no tab characters. Tab stops are assumed to be set every four
	columns (e.g. 1, 5, 9, ...), so that each tab character is replaced by from
	one to four blanks.
EXAMPLE
	Using -> as a visible tab:
	   detab
	   ->col 1->2->34->rest
	   	col 1	2	34	rest
BUGS
	detab is naive about vertical motions and non-printing characters.