Test failures on Ubuntu Linux

A `bowsprit` or `libcheck` bug?

```
$ tests/test-stats 
Running suite(s): stats
--- test_nothing
--- test_derive_01
--- test_gauge_01
--- test_multi_01
25%: Checks: 4, Failures: 3, Errors: 0
/home/vagrant/git/bowsprit/tests/test-stats.c:82:F:stats:test_derive_01:0: Result not equal (expected 1, got 1)
/home/vagrant/git/bowsprit/tests/test-stats.c:125:F:stats:test_gauge_01:0: Result not equal (expected 1, got 1)
/home/vagrant/git/bowsprit/tests/test-stats.c:179:F:stats:test_multi_01:0: Result not equal (expected 10, got 10)
```