patch 9.1.0147: Cannot keep a buffer focused in a window

Problem:  Cannot keep a buffer focused in a window
          (Amit Levy)
Solution: Add the 'winfixbuf' window-local option
          (Colin Kennedy)

fixes:  #6445
closes: #13903

Signed-off-by: Colin Kennedy <colinvfx@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index 4ae6cc2..bd26e81 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -521,7 +521,7 @@
 	EX_EXTRA|EX_TRLBAR|EX_CMDWIN|EX_LOCK_OK,
 	ADDR_NONE),
 EXCMD(CMD_drop,		"drop",		ex_drop,
-	EX_FILES|EX_CMDARG|EX_NEEDARG|EX_ARGOPT|EX_TRLBAR,
+	EX_BANG|EX_FILES|EX_CMDARG|EX_NEEDARG|EX_ARGOPT|EX_TRLBAR,
 	ADDR_NONE),
 EXCMD(CMD_dsearch,	"dsearch",	ex_findpat,
 	EX_BANG|EX_RANGE|EX_DFLALL|EX_WHOLEFOLD|EX_EXTRA|EX_CMDWIN|EX_LOCK_OK,