Bump lower bounds on versions of base, fingertree.

I've bumped the lower bounds of the versions of base and fingertree.

- base: I don't think I've ever compiled this package using
  a GHC with base 3, so there isn't much point in permitting
  version 3 as the lower bound

- fingertree: it's gone from version 0.0.1 to 0.1.0 which
  suggests some substantial improvement, so I thought I'd
  bump the version

Several packages, like bytestring, that are in the Haskell Platform
have upper bounds that are lower than the current Haskell Platform
versions (2013.2.0.0). However, I've decided to leave the bounds
as they are for now. I've also kept version upper bounds except
for those packages where I'm using version equality. I may relax
those equality constraints, and may do away with the upper bounds
entirely at some point, but I think I'll stop fiddling with
versions for a while.