Add new VC methods: vc-log-incoming and vc-log-outgoing.

Add new VC methods: vc-log-incoming and vc-log-outgoing.
* vc.el (vc-print-log-setup-buttons): New function split out from
vc-print-log-internal.
(vc-log-internal-common): New function, a parametrized version of
vc-print-log-internal.
(vc-print-log-internal): Just call vc-log-internal-common with the
right arguments.
(vc-incoming-outgoing-internal):
(vc-log-incoming, vc-log-outgoing): New functions.
(vc-log-view-type): New permanent local variable.

* vc-hooks.el (vc-menu-map): Bind vc-log-incoming and vc-log-outgoing.

* vc-bzr.el (vc-bzr-log-view-mode): Use vc-log-view-type instead
of the dynamic bound vc-short-log.
(vc-bzr-log-incoming, vc-bzr-log-outgoing): New functions.

* vc-git.el (vc-git-log-outgoing): New function.
(vc-git-log-view-mode): Use vc-log-view-type instead
of the dynamic bound vc-short-log.

* vc-hg.el (vc-hg-log-view-mode): Use vc-log-view-type instead
of the dynamic bound vc-short-log.  Highlight the tag.
(vc-hg-log-incoming, vc-hg-log-outgoing): New functions.
(vc-hg-outgoing, vc-hg-incoming, vc-hg-outgoing-mode):
(vc-hg-incoming-mode): Remove.
(vc-hg-extra-menu-map): Do not bind vc-hg-incoming and vc-hg-outgoing.