Finish the Bug#11728 work: hg & git

Finish the Bug#11728 work: hg & git

* lisp/vc/vc-git.el (vc-git--pushpull): Make `extra-args' a list.
Do not set `compilation-error-regexp-alist', this is done in
`vc-compilation-mode'.
(vc-git-error-regexp-alist): Tweak the regexp.
* lisp/vc/vc-hg.el (vc-hg-error-regexp-alist): Make non-trivial.
(vc-hg--pushpull): Accept `post-processing' argument.
Call them after the `command'.
(vc-hg-pull): Pass the `post-processing' commands that show which
are to be modified by the `update', and then run `update'.