test: modernize funny-names test style

This is one of the early tests, so it uses a style that by modern
standards can be hard to read.  Tweak it to:

 - clearly declare what assertion each test is designed to check

 - mark tests that create state later tests will depend on with the
   word "setup" so people writing or running tests know the others
   can be skipped or reordered safely

 - put commands that populate a file with expected output inside
   the corresponding test stanza, so it is easier to see by eye
   where each test begins and ends

 - instead of pipelines, use commands that read and write a
   temporary file, so bugs causing commands to segfault or produce
   the wrong exit status can be caught.

More cosmetic changes:

 - put the opening quote starting each test on the same line as the
   test_expect_* invocation, and indent the commands in each test
   with a single tab

 - end the test early if the underlying filesystem cannot
   accomodate the filenames we use, instead of marking all tests
   with the same TABS_IN_FILENAMES prerequisite.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>