patch 8.0.0552: toupper and tolower don't work properly for Turkish

Problem:    Toupper and tolower don't work properly for Turkish when 'casemap'
            is empty. (Bjorn Linse)
Solution:   Check the 'casemap' options when deciding how to upper/lower case.
diff --git a/src/version.c b/src/version.c
index 2ea5708..e37178b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    552,
+/**/
     551,
 /**/
     550,