Iron Golems can spawn if mob spawning gamerule is false

Verification builds: 1.2.5

Summary: When the conditions are met for an Iron Golem to spawn (in a village, or village-like structure with villagers around) it will spawn in even if the gamerule domobspawning is false.

Impact: If domobspawning is set to false, the expectation is that no mobs will spawn unless explicitly done so by commands or spawn eggs.

Repro Steps:

1. Create a new world with cheats enabled and mob spawning disabled.
2. Use /say @e to verify there are no entities in the world, if there are do /kill @e[type=!player]
3. Now build some wooden box houses and add plenty of doors to the sides of them.
4. Use a villager spawn egg to spawn in some villagers
5. Wait patiently for an Iron Golem to spawn. I used a repeating command block to testfor @e[type=iron_golem]

Observed Results: Iron Golems spawn even if mob spawning is disabled

Expected Results: Iron Golems should not spawn unless mob spawning is enabled and the "village" meets the requirements for them to spawn

Screenshots/Videos attached: no, but I can make a video if needed!

Notes: It can take a few minutes for the Iron Golem to spawn. Building more wooden boxes may help.