patch 8.1.1791: 'completeslash' also applies to globpath()

Problem:    'completeslash' also applies to globpath().
Solution:   Add the WILD_IGNORE_COMPLETESLASH flag. (test by Yasuhiro
            Matsumoto, closes #4760)
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index fedb38a..e48a72c 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -1,3 +1,4 @@
+source check.vim
 
 " Test for insert expansion
 func Test_ins_complete()
@@ -334,15 +335,11 @@
 
 " Test for insert path completion with completeslash option
 func Test_ins_completeslash()
-  if !has('win32')
-    throw 'Skipped: only works on MS-Windows'
-  endif
+  CheckMSWindows
   
   call mkdir('Xdir')
-
   let orig_shellslash = &shellslash
   set cpt&
-
   new
   
   set noshellslash
@@ -375,6 +372,11 @@
   %bw!
   call delete('Xdir', 'rf')
 
+  set noshellslash
+  set completeslash=slash
+  call assert_true(stridx(globpath(&rtp, 'syntax/*.vim', 1, 1)[0], '\') != -1)
+
   let &shellslash = orig_shellslash
+  set completeslash=
 endfunc