-A non-nil second (optional) argument FORCE means, if the line
-is too short to reach column COLUMN then add spaces/tabs to get there,
-and if COLUMN is in the middle of a tab character, change it to spaces.
+A value of 'coerce for the second (optional) argument FORCE means if
+COLUMN is in the middle of a tab character, change it to spaces.
+Any other non-nil value means the same, plus if the line is too short to
+reach column COLUMN, then add spaces/tabs to get there.
+