patch 8.1.2182: test42 seen as binary by git diff

Problem:    Test42 seen as binary by git diff.
Solution:   Add .gitattributes file.  Make explicit that 'cpo' does not
            contain 'S'. (Daniel Hahler, closes #5072)
diff --git a/Filelist b/Filelist
index e79cbb7..a2b9f0a 100644
--- a/Filelist
+++ b/Filelist
@@ -4,6 +4,7 @@
 # source files for all source archives
 SRC_ALL =	\
 		.gitignore \
+		.gitattributes \
 		.hgignore \
 		.lgtm.yml \
 		.travis.yml \