Ignore binds payload with nil column in AR log subscriber

This pull request backports commit 77516a7 to `3-2-stable` branch.

Conflict resolution:
- Revert ruby 1.9 style hash to support ruby 1.8
- Do not include 8f59ffce into 3-2-stable

This commit works with `ruby-1.9.3-p362` without any regressions.
But it causes two `RuntimeError: ActiveRecord::Associations::Association` errors at `test_sqlite3` when tested with `ruby-1.8.7-p371`. 

- The full output https://gist.github.com/4490252. 
- A minimum testcase is https://gist.github.com/4490257

It's strange for me, Tested `3-2-stable` branch without my fix, a minimum testcase causes the same `RuntimeError: ActiveRecord::Associations::Association`.