t/Makefile: ensure that paths are valid on platforms we care

t/Makefile: ensure that paths are valid on platforms we care

Some pathnames that are okay on ext4 and on HFS+ cannot be checked
out on Windows. Tests that want to see operations on such paths on
filesystems that support them must do so behind appropriate test
prerequisites, and must not include them in the source tree (instead
they should create them when they run). Otherwise, the source tree
cannot even be checked out.

Make sure that double-quotes, asterisk, colon, greater/less-than,
question-mark, backslash, tab, vertical-bar, as well as any non-ASCII
characters never appear in the pathnames with a new test-lint-* target
as part of a `make test`. To that end, we call `git ls-files` (ensuring
that the paths are quoted properly), relying on the fact that paths
containing non-ASCII characters are quoted within double-quotes.

In case that the source code does not actually live in a Git
repository (e.g. when extracted from a .zip file), or that the `git`
executable cannot be executed, we simply ignore the error for now; In
that case, our trusty Continuous Integration will be the last line of
defense and catch any problematic file name.

Noticed when a topic wanted to add a pathname with '>' in it.  A
check like this will prevent a similar problems from happening in the
future.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>