TEST_SET full and fast

[kalmarek]

If ENV[TEST_SET]==full all tests are run;

by default TEST_SET = fast and the aim is that each test file/type doesn't take more than 10s to test
(at the moment some of them take more than a minute on my laptop).

On travis we can have TEST_SET=full for a specific version (latest stable?) of julia

[alexej-jordan]

intuitively, i would have separate files (e.g. integers_full.jl and integers_fast.jl), so the runtests.jl file only needs to check which tests to run once and include the corresponding files.
on the other hand, the fast test files would be easier to maintain as they are overseeable.

still, i would like to discuss what is important enough to include and what amount of tests with templated types is sufficient.

[saschatimme]

https://github.com/JuliaLang/Pkg.jl/pull/1688/files

[kalmarek]

pretty good find!