Sort lines in region alphabetically by a certain range of columns.
For the purpose of this command, the region BEG...END includes
the entire line that point is in and the entire line the mark is in.
The column positions of point and mark bound the range of columns to sort on.
A prefix argument means sort into REVERSE order.
The variable `sort-fold-case' determines whether alphabetic case affects
the sort order.
Note that `sort-columns' rejects text that contains tabs,
because tabs could be split across the specified columns
and it doesn't know how to handle that. Also, when possible,
it uses the `sort' utility program, which doesn't understand tabs.
Use M-x untabify to convert tabs to spaces before sorting.
(fn REVERSE &optional BEG END)