patch 8.0.1553: cannot see what digraph is used to insert a character

Problem:    Cannot see what digraph is used to insert a character.
Solution:   Show the digraph with the "ga" command. (Christian Brabandt)
diff --git a/src/proto/digraph.pro b/src/proto/digraph.pro
index 3cb7dce..dfadc9d 100644
--- a/src/proto/digraph.pro
+++ b/src/proto/digraph.pro
@@ -1,5 +1,6 @@
 /* digraph.c */
 int do_digraph(int c);
+char_u *get_digraph_for_char(int val);
 int get_digraph(int cmdline);
 int getdigraph(int char1, int char2, int meta_char);
 void putdigraph(char_u *str);