patch 8.2.0516: client-server code is spread out

Problem:    Client-server code is spread out.
Solution:   Move client-server code to a new file. (Yegappan Lakshmanan,
            closes #5885)
diff --git a/src/proto.h b/src/proto.h
index 5d81557..0115c68 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -68,6 +68,7 @@
 # include "change.pro"
 # include "charset.pro"
 # include "cindent.pro"
+# include "clientserver.pro"
 # include "clipboard.pro"
 # include "cmdexpand.pro"
 # include "cmdhist.pro"