Add unbind to v-show (fix #4484)

[defcc]

fix #4484

If element exists in dom tree, will set its display property back.

Apply possible transition if value is false.

[yyx990803]

Thanks @defcc - there are a few issues with this fix: if we always reset the display in unbind, then elements hidden by v-show will be revealed if it is inside an element with a leaving transition. So we need to differentiate between a destroy unbind vs. a patch unbind, and only reset display for patch unbind. Transition check is not necessary for patch unbind because a patch unbind cannot happen to common child of the same <transition> component.

I added a 5th argument to unbind in a977642 (and used your test case)

[defcc]

Thanks for your comment.