[Rev 01] RFR: Improve materialization speed

[Robin Westberg]

> Hi all,
> 
> Please review this change that allows materializing a HostedRepository using a common shared "seed", and make use of it in the PR bot.
> 
> Best regards,
> Robin

The pull request has been updated with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase.

-------------

Added commits:
 - 77890bec: Ensure that both source and target refs are present locally
 - f4bc6a89: Fix build error after merge
 - 612d83ce: Merge remote-tracking branch 'upstream/master' into faster_materialize
 - 4637c1b5: git-pr: do not assume a master branch
 - aac97324: Merge remote-tracking branch 'upstream/master' into faster_materialize
 - 27af764d: Remove unnecessary merge test
 - c73064e6: git-pr: git diff can exit with code 141
 - b0cc35dd: Only check the head commit
 - 099d7153: merge-bot: use correct credentials for listing PRs
 - c3359eff: merge-bot: use correct credentials when creating PR
 - 9958c7e4: git-sync: use ref names instead of hashes
 - 19f5473d: merge-bot: clearer merge messages when merging between repos
 - b5f92284: Avoid running the mailing list bridge too often
 - a57c1319: git-pr: friendly help message when missing action
 - 6e9e58b7: 267: Be more tolerant when parsing mbox files
 - feb2fcc0: Add toString methods to all WorkItems
 - 3cbdfd40: 251: Bypass PR update cache when the cooldown period expires for a bridge candidate
 - 72c721a2: 257: Proper setting of custom fields in Jira issues
 - ca0bc833: 255: Improve git repository health check
 - c08e9a6d: 266: Allow getting commit metadata for a range
 - c80ca805: Do not use pull in merge bot
 - 5c96b1cc: Improve merge bot commit message
 - 28d695ba: Fix git issues with merge bot
 - 6cc53a0c: Fix markdown formatting in /csr command
 - 189ade65: Use very defensive programming in CSRCommand
 - 5632c913: 260: CSR command should handle null resolution
 - ce4ae7b9: Typo in conversion from legacy jcheck conf
 - e31fdac1: Updated after offline review

Changes:
  - all: https://git.openjdk.java.net/skara/pull/411/files
  - new: https://git.openjdk.java.net/skara/pull/411/files/bdd86cbd..77890bec

Webrevs:
 - full: https://webrevs.openjdk.java.net/skara/411/webrev.01
 - incr: https://webrevs.openjdk.java.net/skara/411/webrev.00-01

  Stats: 1162 lines in 48 files changed: 833 ins; 236 del; 93 mod
  Patch: https://git.openjdk.java.net/skara/pull/411.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/411/head:pull/411

PR: https://git.openjdk.java.net/skara/pull/411