Spec: Fixed the docs URL for indices.get and indices.exists
Changed dev-tools/es_release_notes to:
* remove markdown support
* prefer PRs over issues
* include related issues in the list
* always use section headers if there is a header
[STORE] Improve exception from Store.failIfCorrupted

If you have previously corrupted files, this method currently builds an
exception like:
```
    failed engine [corrupted preexisting index]
    failed to start shard
```

Followed by a CorruptIndexException. This commit writes the entire
stacktrace to provide additional information. It also changes the
failure message from `corrupted preexisting index` to `preexisting
corrupted index` to prevent confusion.

Closes #7596