add +terminfo use flag to haskeline ebuilds

``` irc
<hypnocat> when trying to emerge dev-haskell/haskeline-0.6.4.6-r1 i get an error:  "*** Warning: running on POSIX but not building the terminfo backend. *** You may need to install the terminfo package manually, e.g. with "cabal install terminfo"; or, use "-fterminfo" when configuring or installing this package."
<hypnocat> but i just installed dev-haskell/terminfo-0.3.2.5
<hypnocat> any ideas on what i should do to get this to work?  should i try the manual "cabal install terminfo" as the error recommends?
<Heather> I doubt
<Heather> hypnocat though it must be a use flag
```