EDG.selector focus jumps unexpectedly

[Evan]

1. Open dojox/grid/tests/enhanced/test_enhanced_grid_selector.html.
   
2. Click on a header column, such as, "Year".
   
3. Click on the same header column again.
   

   The focus (dotted border) moves to the first column, in this example, "Identity".
   

This is annoying when having horizontal scrollbar and clicked on a far right column, as it causes the grid scroll back to the left.

[Evan]

In [27971]:

Fixes #14864, !strict, header focus shouldn't jump when clicking the same column multiple times, also back port to 1.7.x branch

[Evan]

In [27972]:

Refs #14864, !strict, backport the fix to 1.6 branch