RFR: JDK-8016524: [macosx] Bottom line is not visible for JTableHeader [v5]

[Harshitha Onkar]

> Previously, the JTableHeader Bottom line wasn't visible on MacOS LAF (Aqua). With the fix the bottom line (light grey) is visible. 
> 
> Changes were made to AquaTableHeaderBorder.paintBorder method and the height of the component+border was adjusted in paint method.
> 
> A new test case (JTHeaderBorderTest.java) was added to test the fix as there was no corresponding test case present for this issue previously. The test checks if the border is visible by checking the color at the border location with the background color of the table and table-header, if both are different test case passes and it fails if the pixel color at border location matches either the table-header or table background color.

Harshitha Onkar has updated the pull request incrementally with one additional commit since the last revision:

  changed the test case condition and marked the test as mac-only

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7219/files
  - new: https://git.openjdk.java.net/jdk/pull/7219/files/516985d5..552d4099

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7219&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7219&range=03-04

  Stats: 46 lines in 1 file changed: 26 ins; 12 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7219.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7219/head:pull/7219

PR: https://git.openjdk.java.net/jdk/pull/7219