Zerokey to Delkey for button reset

I use pen and tablet and sometimes I leave my cursor over some input field and I try to switch to Camera View by pressing zero. Result is that I unintentionally reset that field.
That isn't a problem when I reset simple numeric field, but I have managed to reset quite complex python expressions so I've decided to change that ZEROKEY to something less used like DELKEY.

I have noticed that this handler does not use default reset operator and because of that undo doesn't work always after reseting so I have corrected that.

[brechtvl, 2011-05-25 11:01:42]

In this patch the option to reset all or only a single element in an array using
ctrl key is lost, that should be added back. Further looks good to me.

[Damir Prebeg, 2011-05-31 07:49:55]

Patch cleaned, array reset returned. Del resets active botton and ctrl+del a
whole array

[brechtvl, 2011-05-31 09:56:53]

Committed, thanks for the patch.