Run tests on Travis

[RyanGlScott]

Currently, the test suite isn't run on Travis builds. This PR aims to fix that. I had to make some modifications to make this happen:

• Unfortunately, HUnit (which we depend on for the test suite) depends on deepseq, so trying to naïvely run cabal install --only-dependencies --enable-tests will result in a dependency cycle. To get around this, I have to manually specify the dependencies in .travis.yml à la binary.
• Also unfortunately, there's a Safe Haskell bug in GHC 7.2.1 that prevents it from installing transformers without running sudo ghc-pkg trust base. But in order to use sudo, I have to disable the containerized Travis builds. (This isn't true anymore, see Run tests on Travis #24 (comment))
• I needed to bump the upper version bounds on HUnit to < 1.6 to accommodate the HUnit-1.5 release on Hackage. Also, the test suite failed to build without an explicit ghc-prim dependency.

[RyanGlScott]

An addendum to the second point: I opted to keep the containerized Travis builds (which are faster) by simply not running the test suite on GHC 7.2.1, which I think is an acceptable sacrifice.

[hvr]

@RyanGlScott hrm... this is a bit awkward... I was about to convert deepseq to the new-style .travis scripts as the old scripts are too fragile and too complicated. However, new-build has one open issue regarding cyclic dependencies involving the package under test, so we wouldn't be able to build & run the testsuites :-/

[RyanGlScott]

I was about to convert deepseq to the new-style .travis scripts as the old scripts are too fragile and too complicated.

Ah! Well if there's a cleaner way to do this, I'd vastly prefer it over this approach.

However, new-build has one open issue regarding cyclic dependencies involving the package under test, so we wouldn't be able to build & run the testsuites :-/

What issue is that?

[hvr]

What issue is that?

haskell/cabal#3422

(and more discussion can be found at haskell/cabal#3232)

That being said, maybe we should just merge this one, and hope that new-build will become capable of cyclic deps before old-build is killed off for good

[RyanGlScott]

That being said, maybe we should just merge this one, and hope that new-build will become capable of cyclic deps before old-build is killed off for good

That sounds reasonable to me.

Other than the whole cyclic dependency hullabaloo, do you have any objections to bumping the cabal-install versions used in the Travis script for old GHCs? I simply lack the knowledge about old cabal-installs to figure out how to diagnose bugs like these. :\

[hvr]

do you have any objections to bumping the cabal-install versions used in the Travis script for old GHCs?

nope, no objection; with older cabals there were issues requiring us to test with matching cabal versions, but with modern cabal versions this shouldn't be a problem anymore to use the latest cabal release.