Reset Exposure Compensation to 0 on shutdown

[Licaon_Kter]

PR already here: https://bitbucket.org/hudson/magic-lantern/pull-requests/779/add-switch-to-reset-exposure-compensation/diff

A fix for https://bitbucket.org/hudson/magic-lantern/issues/2448/exposure-compensation-display-is-slow somewhat, as at least on (my) EOS M, I find the wheel a pain to use to get EC right (also this does not help https://bitbucket.org/hudson/magic-lantern/issues/2257/selected-wheel-setting-marked ), so having it reset to zero on restart helps me and my shooting style.

Hope it's useful for others too.

Some points that might be up to debate:
* it's ok as CONFIG_INT( hey, it does not error out on compile like this ) instead of static CONFIG_INT?
* is the position in the menu at Prefs/Misc key ok?
* is this working as I think on all cameras?

Thanks

[dfort]

Trying to understand this. Exactly how are you setting up your camera? I usually use full auto or full manual mode and haven't fiddled with exposure compensation. Though I do use auto bracketing which is on the same Canon menu as "Expo.comp."

[Licaon_Kter]

I'm using Av and Tv, so ExpComp comes handy. Now, since I'm not earning my bread shooting, I might be odd.

Also, since (at least on my) EOS M the wheel is finicky (I blame myself too, I used it a lot for those FPS override tests ), I can get it either too easy moved (to + or -) or find it too hard to reset it (to 0), hence this PR.