Split out version detection for 'suse' to 'sles' and 'opensuse'.

Hi Alex,

Until now SUSE Linux Enterprise (SLES) and openSUSE both reported as 'suse'. However I needed to distinguish between the two. Attached is the patch + tests that implements this. Of course this does 'break' people who might expect these distros to report in as 'suse' - I am not sure how to handle this. Do you care about this possible 'breakage'? of course reporting 'sles' and 'opensuse' is arguably more correct.