Implement alternate exit codes to comply with Pacemaker and DRBD directly.
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=head2 C<-c [rhcs|drbd|crm]>, C<caller=[rhcs|drbd|crm]>

Default is C<rhcs>

This controls C<fence_na>'s exit codes and operation, depending on the caller. 

=head3 C<rhcs>

In this mode, C<fence_na> operates in accordance with the C<FenceAgentAPI> as used by Red Hat Cluster Services. Please see L<https://fedorahosted.org/cluster/wiki/FenceAgentAPI>.

=head3 C<drbd>

In this mode, C<fence_na> operates in accordance with the DRBD specifications. Please see L<http://www.drbd.org/users-guide/s-fence-peer.html>.

=head3 C<crm>

In this mode, C<fence_na> operating in accordance with the Pacemaker fence API. 
* See: http://hg.linux-ha.org/glue/file/27900edc25d9/lib/plugins/stonith/external (sbd and getconfignames)
22:31 < tserong> see also the return codes in http://hg.linux-ha.org/glue/file/27900edc25d9/include/stonith/stonith.h
22:31 < tserong> i assume this is all still accurate
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