digest: fix CURLAUTH_DIGEST_IE

The URI that is passed in as part of the Authorization: header needs to
be cut off at '?' if CURLAUTH_DIGEST_IE is set. Previously the code only
did when calculating the MD5sum.

Bug: http://curl.haxx.se/bug/view.cgi?id=1308
Patched-by: Sergey Tatarincev