patch 8.0.1748: CmdlineEnter command uses backslash instead of slash

Problem:    CmdlineEnter command uses backslash instead of slash.
Solution:   Don't treat the character as a file name. (closes #2837)

src/fileio.c

@@ -9524,6 +9524,12 @@ apply_autocmds_group(
 	 * ColorScheme, QuickFixCmd* or DirChanged */
 	if (event == EVENT_FILETYPE
 		|| event == EVENT_SYNTAX
+		|| event == EVENT_CMDLINECHANGED
+		|| event == EVENT_CMDLINEENTER
+		|| event == EVENT_CMDLINELEAVE
+		|| event == EVENT_CMDWINENTER
+		|| event == EVENT_CMDWINLEAVE
+		|| event == EVENT_CMDUNDEFINED
 		|| event == EVENT_FUNCUNDEFINED
 		|| event == EVENT_REMOTEREPLY
 		|| event == EVENT_SPELLFILEMISSING
@@ -9532,7 +9538,10 @@ apply_autocmds_group(
 		|| event == EVENT_OPTIONSET
 		|| event == EVENT_QUICKFIXCMDPOST
 		|| event == EVENT_DIRCHANGED)
+	{
 	    fname = vim_strsave(fname);
+	    autocmd_fname_full = TRUE; /* don't expand it later */
+	}
 	else
 	    fname = FullName_save(fname, FALSE);
     }

src/testdir/test_autocmd.vim

@@ -837,6 +837,8 @@ func Test_Cmdline()
   au! CmdlineEnter
   au! CmdlineLeave
 
+  let save_shellslash = &shellslash
+  set noshellslash
   au! CmdlineEnter / let g:entered = expand('<afile>')
   au! CmdlineLeave / let g:left = expand('<afile>')
   let g:entered = 0
@@ -849,6 +851,7 @@ func Test_Cmdline()
   bwipe!
   au! CmdlineEnter
   au! CmdlineLeave
+  let &shellslash = save_shellslash
 endfunc
 
 " Test for BufWritePre autocommand that deletes or unloads the buffer.

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1748,
 /**/
     1747,
 /**/