t3010: update to demonstrate "ls-files -k" optimization pitfalls
t3010: update to demonstrate "ls-files -k" optimization pitfalls

An earlier draft of the previous step used cache_name_exists() to
check the directory we were looking at, which missed the second case
described in its log message.  Demonstrate why it is not sufficient.

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git