New command: revdep-reinstall

* Request re-installing reverse dependencies of a formula.
  - When a formula receives a major update, its libraries usually have
    a major version bump or their symbol tables usually change, both of
    which may break other formulae that dynamically linking to those
    libraries. This problem can be solved by rebuilding those formulae,
    and this command helps in this situation.
* Rework reinstall command to have a standalone function to make
  external usage easier.
Remove controversial revdep-reinstall command.