RFR: JDK-7154070: in SwingSet2, switching between LaFs it's easy to lose JTable dividers [v6]

[Prasanta Sadhukhan]

> In SwingSet2 in TableDemo, we can see grid dividers in Metal L&F but 
> if we Switch to the Nimbus LaF which has no grid dividers by default and then if we switch to Java (Metal): it will show no dividers.
> 
> Issue is Nimbus call JTable.showGrid(false) in installDefaults but fail to reset in uninstallDefaults which is now rectified.
> 
> No regression test is added as it can be verified by SwingSet2 Tabledemo..

Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:

  Fix and test updated

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12385/files
  - new: https://git.openjdk.org/jdk/pull/12385/files/1a456cc7..b10f6c2d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12385&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12385&range=04-05

  Stats: 22 lines in 2 files changed: 3 ins; 14 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/12385.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12385/head:pull/12385

PR: https://git.openjdk.org/jdk/pull/12385