'C-1 C-x v L' asks for revision and shows its log entry with diff (bug#38044)
* doc/emacs/maintaining.texi (VC Change Log): Explain the numeric prefix arg of 'C-x v L' (vc-print-root-log). * lisp/vc/vc-git.el (vc-git-print-log): Add command line option "-p" when vc-log-view-type is 'with-diff'. (vc-git-log-view-mode): Use long style when vc-log-view-type is 'with-diff'. * lisp/vc/vc.el (vc-print-log-internal): Add optional arg 'type'. (vc-log-internal-common): Use 'region-history-mode' when type is 'with-diff' and backend supports 'region-history-mode'. (vc-print-root-log): Add optional arg 'revision'. In interactive spec read a revision when current-prefix-arg is 1. Use current-prefix-arg "as is" when it is a number. Show revision in long style with diff when limit is 1 and revision is non-nil.