patch 8.2.3184: cannot add a digraph with a leading space

Problem:    Cannot add a digraph with a leading space.  It is not easy to list
            existing digraphs.
Solution:   Add setdigraph(), setdigraphlist(), getdigraph() and
            getdigraphlist(). (closes #8580)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 62d50b2..9eb423e 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -9315,7 +9315,7 @@
     else
 	listdigraphs(eap->forceit);
 #else
-    emsg(_("E196: No digraphs in this version"));
+    emsg(_(e_no_digraphs_version));
 #endif
 }