TAP tests are badly named

We should describe test sets by what they test, not by how they test.
TAP is a testing tool/protocol. The current set of tests we have test
the programs in src/bin, and we should really name the test set by a
name that reflects that, rather than the fact that we are using TAP
tools to run the tests. What if we decide to test something else using
TAP? Would we call that set of tests TAP tests too?

--enable-tap-tests is a reasonable configuration setting, because it's
about whether or not we have a TAP testing framework available, but I
think we should stop calling the bin tests "TAP tests" and we should
change the test name in vcregress.pl to a more appropriate name. In the
buildfarm I'm calling the step "bin-check":
<http://www.pgbuildfarm.org/cgi-bin/show_stage_log.pl?nm=crake&dt=2015-07-30%2012%3A25%3A58&stg=bin-check>

Thoughts?

cheers

andrew