Commented Feature: Allow DbContext to be created with an already-open existing connection plus ensure connection closing is consistent with opening [45]

This item was migrated from the DevDiv work item tracking system [ID=7992]. <br />
Comments: Checked in change #56e510c. Updated EntityConnection State so it now tracks the underlying store connection State. This is a breaking change as we will now report a different (but more consistent) state for the EntityConnection.