Backport incompatible libruby check
Please backport r50410, r50412, and r50413, to get rid of frequently reported stale bugs.
These changes raise an exception when an extension library linked to an incompatible ruby is loaded.
and the patches pointed by nobu are totally broken,
only r50416 is needed but the diff is on the assumption of r50410-r50515.
- Backport changed from 2.0.0: REQUIRED, 2.1: REQUIRED, 2.2: REQUIRED to 2.0.0: REQUIRED, 2.1: DONE, 2.2: REQUIRED
ruby_2_1 r50469 merged revision(s) 50416.
- Backport changed from 2.0.0: REQUIRED, 2.1: DONE, 2.2: REQUIRED to 2.0.0: REQUIRED, 2.1: DONE, 2.2: DONE
r50410, r50412, r50413, r50414, r50415 and r50416 were backported into
ruby_2_2 at r50486.
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