patch 9.0.1227: no cmdline completion for :runtime

Problem:    No cmdline completion for :runtime.
Solution:   Add completion for :runtime. (closes #11853, closes #11447)
            Improve the resulting matches.
diff --git a/src/vim.h b/src/vim.h
index 7d58b06..930b17b 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -811,6 +811,7 @@
 #define EXPAND_DISASSEMBLE	50
 #define EXPAND_BREAKPOINT	51
 #define EXPAND_SCRIPTNAMES	52
+#define EXPAND_RUNTIME		53
 
 // Values for exmode_active (0 is no exmode)
 #define EXMODE_NORMAL		1
@@ -2661,6 +2662,7 @@
 #define DIP_NORTP   0x20	// do not use 'runtimepath'
 #define DIP_NOAFTER 0x40	// skip "after" directories
 #define DIP_AFTER   0x80	// only use "after" directories
+#define DIP_PRNEXT  0x100	// for print also file extension
 
 // Lowest number used for window ID. Cannot have this many windows.
 #define LOWEST_WIN_ID 1000