Add support for base-4.6 (ghc-7.6)

[bitc]

HTTP currently does not build with base-4.6, which is to be included with ghc-7.6

The problem is that Prelude.catch was removed from base: it is now required to use Control.Exception.catch.

This pull request replaces all uses of Prelude.catch with Control.Exception.catch (thanks to https://github.com/hesselink/HTTP/tree/feature/new-exceptions) , and bumps the upper bound dependency of base to < 4.7

This probably breaks compatibility with old versions of base(3 and below), so some further preprocessor magic may be necessary.

[hsenag]

Thanks for the fixes. Do they build for you? With GHC 7.6.RC1, I'm getting a problem with the auto-generated Paths_HTTP trying to use catch from the Prelude, which is odd since presumably Cabal should be responsible for that and I've got the Cabal that comes with GHC.

[hsenag]

Never mind, turned out it's cabal-install responsible for that and I had an old version.

[hsenag]

OK, so GHC 6.10 at least will require preprocessor magic. I'll see if the proposal on ghc-users to make hiding a non-existent import is going to go into 7.6 before deciding what to do.

[hsenag]

I've applied the base bump independently and released HTTP 4000.2.4.

I still can't get the test harness to build on GHC 7.6 (because of dependencies not being updated) so haven't yet updated that to claim 7.6 support.

Thanks for getting the ball rolling!