Fix interaction between vc-hg find-file-hook and vc state caching

Fix interaction between vc-hg find-file-hook and vc state caching

Bad assumptions in the `vc-hg-find-file-hook' prevented it from
working. This correctly them.  (Bug#33129).

2018-10-23  Daniel Pittman  <slippycheeze@google.com>

	* lisp/vc/vc-hg.el (vc-hg-find-file-hook): This function made two
	assumptions about conflicted files that were not accurate,
	preventing conflicts in files ever being detected.

	The first was that the `vc-state' was cache by the time this was
	invoked, which it is not - at least when visiting the file, or
	using `vc-refresh-state'.

	The second was that a file with the ".orig" extension would be
	present, next to the file being visited.  This is the default
	behavior of Mercurial, but can be overridden by the user.

	Since the VC mode-line code will shortly calculate the state for
	display, the optimization of testing for the ".orig" file only
	delayed this work by a few moments.