Replace the built-in "test" target with "check".

The built-in "test" target has few issues that cannot be fixed:

- It does not depend on the test executables, so you must run "make" and
  "make test".
- It does not print errors from failed tests by default. The workaround
  is to run "make test ARGS=--output-on-failure".

This patch add a new "check" target that fix both issues.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>