walkDirRec
Hi the walkDirRec function doesn't seem to work in a GET request.
If I do this

```
import os, re, jester, asyncdispatch, htmlgen, asyncnet


routes:

  get "/":
    var html = ""
    html.add "<form action=\"upload\" method=\"post\"enctype=\"multipart/form-data\">"
    html.add "<input type=\"file\" name=\"file\"value=\"file\">"
    html.add "<input type=\"submit\" value=\"Submit\" name=\"submit\">"
    html.add "</form>"
    html.add "<h3>Folder</h3>"
    for file in walkDirRec("./"):
      html.add "<li><a href=\"" &file & "\">" & file & "</li>"
    resp(html)

runForever()

```

i get

```
/nimcache/posix.c:103:18: error: invalid application of 'sizeof' to an incomplete type 'DIR' (aka 'struct __dirstream')
NTI103214.size = sizeof(DIR);
                 ^     ~~~~~
/usr/include/dirent.h:127:16: note: forward declaration of 'struct __dirstream'
typedef struct __dirstream DIR;
               ^
1 error generated.
Error: execution of an external program failed
```

Am I doing something wrong or is this a bug?

Greetings Jakob
