t4011: modernise style

t4011: modernise style

Match the style to more modern test scripts, namely:

 - The first line of each test has prereq, title and opening sq for the
   script body.  This makes the test shorter while reducing the need for
   backslashes.

 - Be prepared for the case in which the previous test may have failed.
   If a test wants to start from not having "frotz" that the previous test
   may have created, write "rm -f frotz", not "rm frotz".

 - Prepare the expected output inside your own test.

 - The order of comparison to check the result is "diff expected actual",
   so that the output will show how the output from the git you just broke
   is different from what is expected.

 - Write no SP between redirection '>' (or '<' for that matter) and the
   filename.

Signed-off-by: Junio C Hamano <gitster@pobox.com>