error_resolve_conflict: rewrap advice message

error_resolve_conflict: rewrap advice message

If you try to commit with unresolved conflicts in the index,
you get this message:

	$ git commit
	U       foo
	error: 'commit' is not possible because you have unmerged files.
	hint: Fix them up in the work tree,
	hint: and then use 'git add/rm <file>' as
	hint: appropriate to mark resolution and make a commit,
	hint: or use 'git commit -a'.
	fatal: Exiting because of an unresolved conflict.

The irregular line-wrapping makes this awkward to read, and
it takes up more lines than necessary. Instead, let's rewrap
it to about 60 characters per line:

	$ git commit
	U       foo
	error: 'commit' is not possible because you have unmerged files.
	hint: Fix them up in the work tree, and then use 'git add/rm <file>'
	hint: as appropriate to mark resolution and make a commit, or use
	hint: 'git commit -a'.
	fatal: Exiting because of an unresolved conflict.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>