Break up long test suites

[dpsanders]

To deal with the (hopefully temporary) issue JuliaLang/julia#15346, we should break up the long test suites (say, longer than 100 tests) into sub-parts.

[lbenet]

I've checked where the tests are hanging: locally, it is in the pow tests of the ITF1788 suite, though travis hangs elsewhere (after sqrt). My point is that our own tests run nicely. So perhaps it is enough to add an if requiring v0.4 in order to check the ITF1788 test suite, so v0.5 will not check them. Eventually, when v0.5 gets stabilized, we should take away that if and test everything.

How do you like this idea?

[dpsanders]

Great idea! I'll do that.

[dpsanders]

@cpierard: Would you like to try doing this?

[dpsanders]

In particular this file: https://github.com/dpsanders/ValidatedNumerics.jl/blob/master/test/ITF1788_tests/libieeep1788_tests_elem.jl