patch 8.0.1176: job_start() does not handle quote and backslash correctly

Problem:    Job_start() does not handle quote and backslash correctly.
Solution:   Remove quotes, recognize and remove backslashes.

src/os_unix.c

@@ -4074,7 +4074,7 @@ wait4pid(pid_t child, waitstatus *status)
 mch_parse_cmd(char_u *cmd, int use_shcf, char ***argv, int *argc)
 {
     int		i;
-    char_u	*p;
+    char_u	*p, *d;
     int		inquote;
 
     /*
@@ -4092,26 +4092,34 @@ mch_parse_cmd(char_u *cmd, int use_shcf, char ***argv, int *argc)
 	    if (i == 1)
 		(*argv)[*argc] = (char *)p;
 	    ++*argc;
+	    d = p;
 	    while (*p != NUL && (inquote || (*p != ' ' && *p != TAB)))
 	    {
 		if (p[0] == '"')
+		    /* quotes surrounding an argument and are dropped */
 		    inquote = !inquote;
-		else if (p[0] == '\\' && p[1] != NUL)
+		else
+		{
+		    if (p[0] == '\\' && p[1] != NUL)
 		    {
 			/* First pass: skip over "\ " and "\"".
 			 * Second pass: Remove the backslash. */
-		    if (i == 1)
-			mch_memmove(p, p + 1, STRLEN(p));
-		    else
 			++p;
 		    }
+		    if (i == 1)
+			*d++ = *p;
+		}
 		++p;
 	    }
 	    if (*p == NUL)
-		break;
+	    {
 		if (i == 1)
-		*p++ = NUL;
+		    *d++ = NUL;
-	    p = skipwhite(p);
+		break;
+	    }
+	    if (i == 1)
+		*d++ = NUL;
+	    p = skipwhite(p + 1);
 	}
 	if (*argv == NULL)
 	{

src/testdir/test_channel.vim

@@ -1590,6 +1590,22 @@ func Test_collapse_buffers()
   bwipe!
 endfunc
 
+func Test_cmd_parsing()
+  if !has('unix')
+    return
+  endif
+  call assert_false(filereadable("file with space"))
+  let job = job_start('touch "file with space"')
+  call WaitFor('filereadable("file with space")')
+  call assert_true(filereadable("file with space"))
+  call delete("file with space")
+
+  let job = job_start('touch file\ with\ space')
+  call WaitFor('filereadable("file with space")')
+  call assert_true(filereadable("file with space"))
+  call delete("file with space")
+endfunc
+
 func Test_raw_passes_nul()
   if !executable('cat') || !has('job')
     return

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1176,
 /**/
     1175,
 /**/