Incompatible is less serious.

Ensure that the message regarding incompatible nodes is explicitly
clear and doesn't trigger errors.

This is necessary because even in a pure 1.4.1 cluster, depending on
how nodes are started capability negotation might take a few seconds,
where some nodes will be shown as incompatible.
Merge pull request #135 from basho/csm-clarify-incompatibility-1.4

Incompatible is less serious. (1.4.1)