filter_get: back out changes which increased memory footprint…

…to deleterious levels on MacOS clients.
Correct fix is to queue and serialise column requests.
New release tag humpub-release-78-06

Generated by /nfs/users/nfs_m/mca/gitwk-anacode/team_tools.stable/otterlace/release/scripts/otterlace_release_tag (otter/75-102-g07ad386 from intcvs1:/repos/git/anacode/team_tools.git)