erasure-code: check plugin version when loading it
When loading the erasure code plugin, check the Ceph version against which it was built and fail if it does not match. A given plugin will work with a given version of Ceph only and if this check is not done it will crash the daemon instead of reporting a human readable error. See http://tracker.ceph.com/issues/9153 for an example of such failure.
erasure-code: add Ceph version check to plugins
Add the __erasure_code_version function to all plugins, to return the
Ceph version against which they have been compiled. When a plugin is
loaded, an error is thrown if the version of the plugin does not match
the version of the daemon loading it.
If the symbol does not exist, which will be true of older plugins, set
the version to "an older version" so it never matches.
Signed-off-by: Loic Dachary <email@example.com>