From: Derrick Stolee <dstolee@microsoft.com>

b9660c1 (dir: fix checks on common prefix directory, 2019-12-19)
modified the way pathspecs are handled when handling a directory
during "git clean -f <path>". While this improved the behavior
for known test breakages, it also regressed in how the clean
command handles cleaning a specified file.

Add a test case that demonstrates this behavior. This test passes
before b9660c1 then fails after.

Helped-by: Kevin Willford <Kevin.Willford@microsoft.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

Submitted-As: https://lore.kernel.org/git/pull.526.git.1579119946211.gitgitgadget@gmail.com