Pulls in these changes:
 - *: use errors.Errorf in replace of fmt.Errorf
 - *: use github.com/cockroachdb/errors
 - vendor: add cockroachdb/errors and its dependencies
 - *: add FileNum type
 - db: delete orphaned temporary files in Open
 - version_set: Handle case where RocksDB doesn't bump minUnflushedLogNum
 - db: modify Options.DebugCheck to be a function
 - internal/manifest: Relax SeqNum overlap invariant in L0
 - internal/metamorphic: fix ingest_using_apply implementation
 - *: use Go 1.13 error wrapping
 - internal/metamorphic: randomize MaxConcurrentCompactions
 - internal/metamorphic: enable run comparison by default
 - internal/metamorphic: temporarily disable ingest_using_apply
 - db: document that Close may not be called twice
 - db: use require.* functions for test checks
 - *: use require.NoError everywhere
 - internal/errorfs: move to new package

Release note: None