Fix several migration issues with the Task/Counter patch

Summary:
People hit three issues with D3914:

• As per T2059, we applied a schema change from a .php patch, which currently does not work if you use a different user to make schema changes than for normal use.
  • Since the change in question is idempotent, just move it to a .sql patch. We'll follow up in T2059 and fix it properly.
• Rogue daemons at several installs used old code (expecting autoincrement) to insert into the new table (no autoincrement), thereby creating tasks with ID 0.
  • Rename the table so they'll fail.
  • This also makes the code a little more consistent.
• Some installs now have tasks with ID 0.
  • Use checks against null rather than against 0 so we can process these tasks.

The major issues this fixes are the schema upgrade failure in T2059, and the infinite loops in T2072 and elsewhere.

This isn't really a fully statisfactory fix. I'll discuss some next steps in T2072.

Test Plan: Created new tasks via MetaMTA/Differential. Ran tasks with phd debug taskmaster. Inserted a task 0 and verified it ran and archived correctly.

Reviewers: btrahan, vrana, nh

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2072, T2059

Differential Revision: https://secure.phabricator.com/D3973