Use module_exec instead of module_eval whenever having variables

[samnang]

Instead of having to assign a temp local variable to be able to access closure block, should we use module_exec instead?

[coveralls]

Coverage remained the same when pulling 0d6abfe on samnang:use_module_exec into e740fc4 on avdi:master.

[avdi]

I'm convinced :-) Feel free to update other instances of module_exec. Honestly at this point I'm wondering if there's any reason to use module_eval at all in a project that assumes Ruby 1.9+ (and doesn't eval strings).

[avdi]

Er, feel free to update other instances of module_eval, I mean.

[samnang]

@avdi it has been merged, do I have to push to another branch and pull request?