patch 7.4.1154
Problem:    No support for JSON.
Solution:   Add jsonencode() and jsondecode().  Also add v:false, v:true,
            v:null and v:none.
diff --git a/src/proto.h b/src/proto.h
index 2b08eb3..5f52a31 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -95,6 +95,7 @@
 # endif
 # include "hardcopy.pro"
 # include "hashtab.pro"
+# include "json.pro"
 # include "main.pro"
 # include "mark.pro"
 # include "memfile.pro"