RFR: 8281988: Create a regression test for JDK-4618767 [v4]

[Manukumar V S]

> Create a regression test for [JDK-4618767](https://bugs.openjdk.java.net/browse/JDK-4618767)
> 
> Issue identified in [JDK-4618767](https://bugs.openjdk.java.net/browse/JDK-4618767):
> Typing a letter while a JList has focus now makes the selection jump to the first/next node/item whose text starts with that letter even though that letter is accompanied by modifier keys such as ALT or CTRL.
> 
> Fix:
> Only enable JList letter navigation when the user
> doesn't press any modifier keys such as ALT or CTRL.
> 
> Testing:
> I have verified this test with JDK 1.4.0 and JDK 1.4.1 .
> The issue is reproducible using the test with JDK 1.4.0 , where the bug was originally reported and the test passed in JDK 1.4.1 where the issue was fixed.
> I have tested it in Mac and Windows platforms multiple times and it passed everywhere.

Manukumar V S has updated the pull request incrementally with one additional commit since the last revision:

  Fixed review comments: Updated test summary, updated code comments, updated exception message

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7496/files
  - new: https://git.openjdk.java.net/jdk/pull/7496/files/5f9bb9e9..259eb393

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7496&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7496&range=02-03

  Stats: 7 lines in 1 file changed: 1 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7496.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7496/head:pull/7496

PR: https://git.openjdk.java.net/jdk/pull/7496