Do not strip CR when grepping HTTP headers.

By default, MSYS grep reads in text-mode and converts CRLF into LF line
endings. For testing HTTP use binary mode (-U) as checking is done for
CR in HTTP headers

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

t/t5560-http-backend-noserver.sh

@@ -5,6 +5,8 @@ test_description='test git-http-backend-noserver'
 
 HTTPD_DOCUMENT_ROOT_PATH="$TRASH_DIRECTORY"
 
+test_have_prereq MINGW && export GREP_OPTIONS=-U
+
 run_backend() {
 	echo "$2" |
 	QUERY_STRING="${1#*\?}" \