Our cookie are even more broken than I thought.

Ours have spaces in the values. The newer Stringext cookie extraction
doesn't allow this, unlike the previous cohttp version. So rather than
use stringext, use a hand-rolled parser.

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>
Merge pull request #1767 from jonludlam/fix_migration

Our cookie are even more broken than I thought.