DList head/tail -> headOption/tailOption
restored/deprecated existing head/tail; fixed test idiocy
fixed version (duh)
Merge pull request #602 from tpolecat/dlist-fix

DList head/tail -> headOption/tailOption
call-by-need instead of call-by-name in Bind#ifM, Bind#ap
Merge pull request #603 from xuwei-k/call-by-need-bind-methods

call-by-need instead of call-by-name in Bind#ifM, Bind#ap
Merge branch 'scalaz-seven' of github.com:scalaz/scalaz into ilist
tweaks to support 2.9