t0050: Fix merge test on case sensitive file systems

On a case sensitive filesystem, "git reset --hard" might refuse to
overwrite a file whose name differs only by case, even if
core.ignorecase is set.  It is not clear which circumstances cause this
behavior.  This commit simply works around the problem by removing
the case changing file before running "git reset --hard".
Signed-off-by: NSteffen Prohaska <prohaska@zib.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t0050-filesystem.sh

@@ -72,6 +72,8 @@ $test_case 'rename (case change)' '
 
 $test_case 'merge (case change)' '
 
+	rm -f CamelCase &&
+	rm -f camelcase &&
 	git reset --hard initial &&
 	git merge topic