Btest allows running ignored tests

[evantypanski]

Given a btest.cfg file with:

[btest]
IgnoreDirs  = tests

Then some files in tests, if you specify one of the files in tests btest will happily try to run it:

$ btest -d
no tests to execute
$ btest -d tests/test.test
[  0%] tests.test ... failed
  % 'exit 1;' failed unexpectedly (exit code 1)
  % cat .stderr
  cp: /Users/etyp/src/tests/btest/multiple-cfg/btest.tests.cfg: No such file or directory

1 of 1 test failed

Seems like a bug, if it's ignored it shouldn't be added to tests to run, even if it exists. Could cause confusion.