revset: implement a simple 'foo#generations' expression...
revset: implement a simple 'foo#generations' expression
The result of this expression is equivalent to 'foo#g[:]': all reachable
ancestors and descendants of a revset foo.
While not very useful functionality on its own, its implementation can be
tested and revset.relations dict can be easily used by extensions to add other
non-subscript relations.
Differential Revision:
https://phab.mercurial-scm.org/D8394