`require` can be overridden by Angl code

`require` function should be aliased to a different name to prevent it from being overridden by Angl local variables.

On the other hand, lots of Javascript stuff can be overridden by local variables, such as `window`. Perhaps there should be a blacklist for local angl variable names. Any variable with a name on that blacklist becomes an "unnamed" identifier that is assigned a non-blacklist name.

For example, `var window` becomes `var window0`