RFR: 8225181: KeyStore should have a getAttributes method [v5]

[Weijun Wang]

> Add `KeyStore::getAttributes` so that one can get the attributes of an entry without retrieving the entry first. This is especially useful for a private key entry which can only be retrieved with a password.

Weijun Wang has updated the pull request 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. The pull request contains seven additional commits since the last revision:

 - final spec change
 - Merge branch 'master' into 8225181
 - Merge branch 'master' into 8225181
 - redine spec
 - more clear and precise spec
 - clarification on protected attributes
 - 8225181: KeyStore should have a getAttributes method
   
   8225181: KeyStore should have a getAttributes method

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6026/files
  - new: https://git.openjdk.java.net/jdk/pull/6026/files/901bdf83..702168db

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6026&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6026&range=03-04

  Stats: 929909 lines in 2271 files changed: 483097 ins; 432951 del; 13861 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6026.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6026/head:pull/6026

PR: https://git.openjdk.java.net/jdk/pull/6026