Don't consider integer CustomFields as changed when the number doesn't change

Summary: Fixes T4466. We do an excessively strict effect check now, which means that these fields changing from (string) "16" to (int) 16 generates a transaction. Instead, compare integer values if the field has data in it.

Test Plan:

(Also made updates without changing the number, which did not appear in the transaction log anymore.)

Reviewers: btrahan, richardvanvelzen

Reviewed By: richardvanvelzen

CC: aran

Maniphest Tasks: T4466

Differential Revision: https://secure.phabricator.com/D8292