Parameterize Makefile test targets on Python version.

[mulkieran]

Check that dependencies for testing are available.

[mulkieran]

This is a slightly amended version of #120.

The only difference is that test dependencies are stored in variable TEST_DEPENDENCIES and that sort and uniq are used to drop duplicates while non-recursive assignment is used to calculate value of TEST_DEPENDENCIES. This is marginally better because it reports all uninstalled packages in an orderly way. The upside of storing this all in a variable is that the test dependencies only need to be calculated once; the downside is that they need to be calculated at least once always.

Note that even if running tests for python 2, python 3 dependencies are checked. It's hard to get around that w/out doing something really different than grepping the spec file for '^Requires:' lines, and I'm not sure what that really different thing would be.

[atodorov]

ack on my side.

[vpodzime]

Looks good to me too.