Fix versioned namespace atomic clears

When using namespace versioning to achieve atomic cache clears, only
delete cache keys matching the old/current version.

This resolves tag inconsistency issues whereby the process running the
clear would delete keys set against the new version by more recently
spawned concurreny processes. Most seriously this could result in newly
set data keys remaining, but with empty associated tag sets meaning the
invalidation via tags was no longer possible.

created tag 5.0.4

created tag 4.4.4

created tag 4.3.11

[EOM] End of maintenance release for branch 4.3

created tag 5.0.3

created tag 4.4.3

created tag 4.3.10

created tag 3.4.37

created tag 5.0.2

created tag 4.4.2