patch 7.4.2244

Problem:    Adding pattern to ":oldfiles" is not a generic solution.
Solution:   Add the ":filter /pat/ cmd" command modifier.  Only works for some
            commands right now.

src/structs.h

@@ -571,6 +571,7 @@ typedef struct
 # ifdef FEAT_AUTOCMD
     char_u	*save_ei;		/* saved value of 'eventignore' */
 # endif
+    regmatch_T	filter_regmatch;	/* set by :filter /pat/ */
 } cmdmod_T;
 
 #define MF_SEED_LEN	8