t5601-clone: test case-conflicting files on case-insensitive filesystem

A recently introduced regression caused a segfault at clone time on
case-insensitive filesystems when filenames differing only in case are
present. This bug has already been fixed (repository: pre-initialize
hash algo pointer, 2018-01-18), but it's not the first time similar
problems have arisen. Therefore, introduce a test to catch this case and
protect against future regressions.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5601-clone.sh

@@ -573,4 +573,21 @@ test_expect_success 'GIT_TRACE_PACKFILE produces a usable pack' '
 	git -C replay.git index-pack -v --stdin <tmp.pack
 '
 
+hex2oct () {
+	perl -ne 'printf "\\%03o", hex for /../g'
+}
+
+test_expect_success 'clone on case-insensitive fs' '
+	git init icasefs &&
+	(
+		cd icasefs
+		o=$(git hash-object -w --stdin </dev/null | hex2oct) &&
+		t=$(printf "100644 X\0${o}100644 x\0${o}" |
+			git hash-object -w -t tree --stdin) &&
+		c=$(git commit-tree -m bogus $t) &&
+		git update-ref refs/heads/bogus $c &&
+		git clone -b bogus . bogus
+	)
+'
+
 test_done