Fixed: on MS-Windows completion of shell commands didn't work.

runtime/doc/todo.txt

@@ -33,9 +33,6 @@ be worked on, but only if you sponsor Vim development.  See |sponsor|.
 Before release 7.3:
 - Rename vim73 branch to default (hints: Xavier de Gaye, 2010 May 23)
 
-:!cmd completion doesn't work on Windows. (Yue Wu).
-Problem with space in path?
-
 Cursor positioning wrong with 0x200e character. (John Becket, 2010 May 6)
 
 Patch to make more characters work in dialogs. (Yankwei Jia, 2010 Aug 4)

src/ex_docmd.c

@@ -3423,17 +3423,16 @@ set_one_cmd_context(xp, buff)
 	    xp->xp_pattern = bow;
 	xp->xp_context = EXPAND_FILES;
 
-#ifndef BACKSLASH_IN_FILENAME
 	/* For a shell command more chars need to be escaped. */
 	if (usefilter || ea.cmdidx == CMD_bang)
 	{
+#ifndef BACKSLASH_IN_FILENAME
 	    xp->xp_shell = TRUE;
-
+#endif
 	    /* When still after the command name expand executables. */
 	    if (xp->xp_pattern == skipwhite(arg))
 		xp->xp_context = EXPAND_SHELLCMD;
 	}
-#endif
 
 	/* Check for environment variable */
 	if (*xp->xp_pattern == '$'

src/structs.h

@@ -457,8 +457,8 @@ typedef struct expand
 #endif
     int		xp_backslash;		/* one of the XP_BS_ values */
 #ifndef BACKSLASH_IN_FILENAME
-    int		xp_shell;		/* for a shell command more characters
-					   need to be escaped */
+    int		xp_shell;		/* TRUE for a shell command, more
+					   characters need to be escaped */
 #endif
     int		xp_numfiles;		/* number of files found by
 						    file name completion */