tests: don't require strict equality for floats On some architectures (e.g. i386 in Debian), obtaining strictly equal floating-point values is more complex than it looks, leading to test (and therefore build failures):
Expected: 1.400000 Got: 1.400000 FAIL read_dng: Exposure time (../tests/check_dng.c:177)
Instead of requiring equality, we can work around this problem by adding a tolerance on the comparison.
1e-7 is an arbitrary tolerance selected as the lowest working value on the author's test setup.
