Add source data to copier jobs

This allows us to track where a copy job was scheduled from.

Patch by <user name="fu">.
Optimize the sphinx copier

The copier is now resilient and efficient against journals with huge
numbers of comments. It's slightly less efficient with huge numbers of
entries, but it still seems to work fine for all of DW's accounts.

Thanks to <user name="cfud"> and <user name="sixwordstories"> for making
this necessary. :-)