VC: Fix several START-REVISION versus LIMIT issues

VC: Fix several START-REVISION versus LIMIT issues

* lisp/vc/vc-git.el (vc-git-print-log): When LIMIT and
START-REVISION are both supplied, use START-REVISION as the
newest commit, and LIMIT as a base (problem was introduced in
the commit adding 'vc-diff-mergebase' and 'vc-log-mergebase').
* lisp/vc/vc.el (vc-default-log-incoming)
(vc-default-log-outgoing): Fix order of START-REVISION and LIMIT
arguments passed to 'print-log' backend function.
(vc-log-mergebase): Fix order of START-REVISION and LIMIT
arguments passed to 'vc-print-log-internal'.

(cherry picked from commit d23b605f754d07a9abf298353d7d17197094477b)