patch 7.4.774

Problem:    When using the CompleteDone autocommand event it's difficult to
            get to the completed items.
Solution:   Add the v:completed_items variable. (Shougo Matsu)

src/macros.h

@@ -118,6 +118,9 @@
 # define ASCII_ISALNUM(c) (ASCII_ISALPHA(c) || VIM_ISDIGIT(c))
 #endif
 
+/* Returns empty string if it is NULL. */
+#define EMPTY_IF_NULL(x) ((x) ? (x) : (u_char *)"")
+
 /* macro version of chartab().
  * Only works with values 0-255!
  * Doesn't work for UTF-8 mode with chars >= 0x80. */