Revdep check improvements

[krlmlr]

• don't abort if installation of a package fails
• setup() and create() gain "quiet" argument
• fully respect "quiet" argument in remote_download.cran_remote()
• remote_download.cran_remote() explicitly copies file
• trim whitespace for version in remote_metadata.cran_remote()
• install_remotes() shows reason for failure
• list all packages involved in revdep check
• allow existing but empty check_dir
• new system2_check() in preparation for Capture installation output and avoid repeated installation attempts for revdep checks #1300
• cosmetic: on.exit(add = TRUE)
• package_info() works for nonstandard (e.g., local) repositories
• rule() fixes
• update autogenerated test files
• fix tests
• print summary table in README.md and problems.md

NEWS entry:

* Various minor improvements around checking of reverse dependencies
  (#1284, @krlmlr). All packages involved are listed at the start,
  the whole process is now more resilient against package
  installation failures.

* Improved handling of local `file://` repositories in `install()` (#1284, @krlmlr).

* `setup()` and `create()` gain new `quiet` argument (#1284, @krlmlr).

* Print summary table in README.md and problems.md (#1284, @krlmlr).

[hadley]

LGTM