~m,n@T in FORMAT

[David A. Moon <Moon at SCRC-TENEX>]

The description of this in the Laser manual makes no sense.  It says
that ~colrel,colinc@T is equivalent to ~curcol+colrel,colincT where
curcol is the current column.  But assuming colrel isn't negative this
never depends on the value of colinc.  Instead, I implemented this to
move at least colrel columns to the right, and as many additional columns
(possibly none) as required to get to a multiple of colinc.  Is this right?