Add another test re s.has
Don't consume iterator twice
Style fixes
Rewrite DAV storages' encoding behavior

This is more explicit than the old behavior. See
https://github.com/Kozea/Radicale/issues/128 for the discussion that led
to this.
Stricten collection discovery test
Clean up set comparison
Remove DAV header check

iCloud doesn't return anything useful while working fine otherwise.
Skip broken props in get_multi
Refactor!
Merge branch 'encodings'

Conflicts:
	vdirsyncer/storage/dav.py
Deal with case-insensitive servers

See Davmail/Outlook, #113