bash prompt: test the prompt with newline in repository path

bash prompt: test the prompt with newline in repository path

Newlines in the path to a git repository were not an issue for the
git-specific bash prompt before commit efaa0c1532 (bash prompt:
combine 'git rev-parse' executions in the main code path, 2013-06-17),
because the path returned by 'git rev-parse --git-dir' was directly
stored in a variable, and this variable was later always accessed
inside double quotes.

Newlines are not an issue after commit efaa0c1532 either, but it's
more subtle.  Since efaa0c1532 we use the following single 'git
rev-parse' execution to query various info about the repository:

  git rev-parse --git-dir --is-inside-git-dir \
          --is-bare-repository --is-inside-work-tree

The results to these queries are separated by a newline character in
the output, e.g.:

  /home/szeder/src/git/.git
  false
  false
  true

A newline in the path to the git repository could potentially break
the parsing of these results and ultimately the bash prompt, unless
the parsing is done right.  Commit efaa0c1532 got it right, as I
consciously started parsing 'git rev-parse's output from the end,
where each record is a single line containing either 'true' or 'false'
or, after e3e0b9378b (bash prompt: combine 'git rev-parse' for
detached head, 2013-06-24), the abbreviated commit object name, and
all what remains at the beginning is the path to the git repository,
no matter how many lines it is.

This subtlety really warrants its own test, especially since I didn't
explain it in the log message or in an in-code comment back then, so
add a test to excercise the prompt with newline characters in the path
to the repository.  Guard this test with the FUNNYNAMES prerequisite,
because not all filesystems support newlines in filenames.  Note that
'git rev-parse --git-dir' prints '.git' or '.' when at the top of the
worktree or the repository, respectively, and only prints the full
path to the repository when in a subdirectory, hence the need for
changing into a subdir in the test.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>