ksck: add a note about spurious checksum mismatches
ksck: add a note about spurious checksum mismatches

Safe-time isn't properly respected on the server side, which means that
running ksck in 'checksum' mode against an active table generates
spurious checksum mismatches. This just adds a note to that effect so
that users aren't confused.

Change-Id: I85babafb8d264be88dc71c9c878b53dae9c73901
Reviewed-on: http://gerrit.cloudera.org:8080/4341
Tested-by: Kudu Jenkins
Reviewed-by: Mike Percy <e07a1fd797b473a9c849e618aa2ce06d8055760b@apache.org>

helifu/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,andrwng/kudu,andrwng/kudu,helifu/kudu,cloudera/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,andrwng/kudu,InspurUSA/kudu,cloudera/kudu,cloudera/kudu,cloudera/kudu,cloudera/kudu,andrwng/kudu,helifu/kudu,andrwng/kudu,andrwng/kudu,andrwng/kudu,EvilMcJerkface/kudu,cloudera/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,helifu/kudu,EvilMcJerkface/kudu,cloudera/kudu,cloudera/kudu