simplify system call wrapping for cmd.exe

autoload/vundle/installer.vim

@@ -513,14 +513,10 @@ endf
 " return -- the return value from system()
 " ---------------------------------------------------------------------------
 func! vundle#installer#system(cmd) abort
-  " would this suffice?
-  " return system('"'.a:cmd.'"')
   if has("win32") || has("win64")
-    let slash = &shellslash
-    set noshellslash
-    let result = system(shellescape(a:cmd))
-    if slash | set shellslash | endif
-    return result
+    " see cmd.exe docs (scroll down to remarks):
+    " https://technet.microsoft.com/de-de/library/cc771320(v=ws.10).aspx
+    return system('"'.a:cmd.'"')
   else
     return system(a:cmd)
   endif