Merge branch 'vn/revision-shorthand-for-side-branch-log'

Merge branch 'vn/revision-shorthand-for-side-branch-log'

"git log rev^..rev" is an often-used revision range specification
to show what was done on a side branch merged at rev.  This has
gained a short-hand "rev^-1".  In general "rev^-$n" is the same as
"^rev^$n rev", i.e. what has happened on other branches while the
history leading to nth parent was looking the other way.

* vn/revision-shorthand-for-side-branch-log:
  revision: new rev^-n shorthand for rev^n..rev