Make "git help" sort git commands in columns

Make "git help" sort git commands in columns

This changes "pretty_print_string_list()" to show the git commands
alphabetically in column order, which is the normal one.

Ie instead of doing

	git commands available in '/home/torvalds/bin'
	----------------------------------------------
	  add                am                 ...
	  applypatch         archimport         ...
	  cat-file           check-ref-format   ...
	...

it does

	git commands available in '/home/torvalds/bin'
	----------------------------------------------
	  add                diff-tree          ...
	  am                 fetch              ...
	  apply              fetch-pack         ...
	...

where each column is sorted.

This is how "ls" sorts things too, and since visually the columns are much
more distinct than the rows, so it _looks_ more sorted.

The "ls" command has a "-x" option that lists entries by lines (the way
git.c used to): if somebody wants to do that, the new print-out logic
could be easily accomodated to that too. Matter of taste and preference, I
guess.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>