CI for feature branches, too
Merge pull request #2058 from bukzor/buck-cachedproperty

just the @cached_property bit
linting.
fix unsortable error
Merge remote-tracking branch 'buck/buck-ci-for-all' into buck-found-versions
pylint in CI, with grandfathering config
Merge remote-tracking branch 'buck/buck-ci-for-all' into buck-lint
Merge branches 'buck-lint' and 'buck-found-versions' into buck-merge-all

Conflicts:
	pip/index.py
refactor PackageFinder._sort_versions to FoundVersion.sort
added InstalledFinder

had to split out Link and FoundVersion to avoid cyclic imports

Conflicts:
	pip/index.py