clear hold shelf checkin modifier use during checkin broken in 2.8

Evergreen master / 2.8

When using the clear hold shelf checkin modifier on checkin of items, users would get a network error and would not be able to process those items. The error would look like:

Call to [open-ils.circ.checkin] failed for session ... thread trace [1]:\nCan't locate object method \"max_chunk_size\" via package \"OpenSRF::AppSubrequest\" at /usr/local/share/perl/5.14.2/Op​enILS/Application/Circ/Holds.pm line 3630.

This occurs because of changes to Holds.pm in this commit: http://git.evergreen-ils.org/?p=Evergreen.git;a=commit;h=4ccbf980e1f2eadf9f99e015e7ac3d4765d046f2

After some investigation in IRC, a solution was found by changing line 3630 from:

$client->max_chunk_size($chunk_size);

to:

$client->max_chunk_size($chunk_size) if ($client->can('max_chunk_size'));

Working branch forthcoming, along with some other safeguarding of other parts of Holds.pm that were also changed (but may not be broken in the same way).