patch 9.1.1408: not easily possible to complete from register content

Problem:  not easily possible to complete from register content
Solution: add register-completion submode using i_CTRL-X_CTRL-R
          (glepnir)

closes: #17354

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/insexpand.pro b/src/proto/insexpand.pro
index e9ff626..8965aca 100644
--- a/src/proto/insexpand.pro
+++ b/src/proto/insexpand.pro
@@ -17,6 +17,7 @@
 int ctrl_x_mode_line_or_eval(void);
 int ctrl_x_mode_not_default(void);
 int ctrl_x_mode_not_defined_yet(void);
+int ctrl_x_mode_register(void);
 int compl_status_adding(void);
 int compl_status_sol(void);
 int compl_status_local(void);